軽金属学会の学術賞である功績賞の受賞

Country：Japan

科学技術に関する研究開発、理解増進等において顕著な成果を収めた者について、その功績を讃えることにより、科学技術に携わる者の意欲の向上を図り、もって我が国の科学技術水準の向上に寄与することを目的とする科学技術分野の文部科学大臣表彰の賞。

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CRESTプロジェクト（研究代表者：戸田裕之）の成果を国内学会の英文誌に投稿したもの。高分解能TEMやHAADF-STEMといった技法を用い、アルミニウム合金でCuを添加した場合の優れた力学的性質の起源を明らかにした。Cu添加による時効析出物の増加が強度向上や延性低下をもたらすが、それを原子分解能電顕観察で評価し、粒界に沿うナノメートルレベルの無析出物帯の存在や時効析出物の結晶構造の同定などが可能になった。

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表題：『Cast A356 Aluminum Alloy』（M. Kobayashi, K. Uesugi, H. Toda, T. Ohgaki, T. Kobayashi: ）

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論文名：『強加工in-situ複合材料技術を利用した金属切削粉のアップグレードリサイクル』（戸田裕之，澤村純平，小林俊郎）

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躍進賞

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Language：English   Publishing type：Research paper (scientific journal)  

This paper proposes a methodology for surrogate-based microstructural optimization of structural metals that integrates a limited number of 3D image-based numerical simulations with microstructural quantification and coarsening and optimisation processes. The support vector machine that was used had an infill sampling criterion to reduce the number of numerical trials, and the proposed methodology was found to be effective for wrought 2024 aluminium alloy with irregularly shaped particles. Appropriate objective functions were defined to assess particle damage. The number of design parameters, which quantitatively express the size, shape, and spatial distribution of particles, was initially 41, but they were reduced to four during a two-step coarsening process. The surrogate model provided highly accurate predictions, and the size, shape, and spatial distribution values of the optimal and weakest particles were successfully identified. It was shown that the optimal particle was small, spherical, sparsely dispersed, and perpendicular to the loading direction. However, it was also found that the smallest and most independent particle with a spherical shape was not necessarily strong, which implies the effects of particle clustering. It was also concluded that the dependency of in-situ particle strength on size was of crucial importance for weaker particles. The shape and spatial distribution of stronger particles were, however, more crucial for suppressing their internal stress than was their size. The results show that the proposed methodology offers a cost-efficient solution for microstructural designs involving 3D high-fidelity simulations that cannot be obtained with the existing approaches for developing materials.

DOI： 10.1016/j.actamat.2023.119188

Repository Public URL： https://hdl.handle.net/2324/7157956

Language：English   Publishing type：Research paper (scientific journal)  

Hydrogen drastically embrittles high-strength aluminum alloys, which impedes efforts to develop ultrastrong components in the aerospace and transportation industries. Understanding and utilizing the interaction of hydrogen with core strengthening elements in aluminum alloys, particularly nanoprecipitates, are critical to break this bottleneck. Herein, we show that hydrogen embrittlement of aluminum alloys can be largely suppressed by switching nanoprecipitates from the η phase to the T phase without changing the overall chemical composition. The T phase strongly traps hydrogen and resists hydrogen-assisted crack growth, with a more than 60% reduction in the areal fractions of cracks. The T phase-induced reduction in the concentration of hydrogen at defects and interfaces, which facilitates crack growth, primarily contributes to the suppressed hydrogen embrittlement. Transforming precipitates into strong hydrogen traps is proven to be a potential mitigation strategy for hydrogen embrittlement in aluminum alloys.

DOI： 10.1038/s41467-022-34628-4

Repository Public URL： https://hdl.handle.net/2324/6792836

Language：English   Publishing type：Research paper (scientific journal)  

The pursuit of strong and ductile Al alloys with superior resistance to hydrogen embrittlement (HE) is practically significant across the aerospace and transportation industries among others. Unfortunately, effective ways to progress on the strength-HE trade-off for Al-alloys remain elusive. A strategy of suppressing HE by introducing intermetallic compound (IMC) particles to achieve hydrogen redistribution in various trapping sites was proposed. Here, we systematically induce the precipitation of a constant volume fraction of intermetallic compound (IMC) particles by adding one of 14 elements in a ternary Al-Zn-Mg high-strength alloy. We show a strong correlation between hydrogen trapping energies of the IMC obtained from ab initio calculations with the resistance to HE. Mn-rich Al11Mn3Zn2 particles exhibit the highest hydrogen trapping energy (0.859 eV/atom), leading to a decrease by approximately 5 orders of magnitude in the hydrogen occupancy in η2 (MgZn2) phase interfaces and grain boundaries, where HE cracks initiate. The Mn-addition did not deteriorate the ductility and most Al11Mn3Zn2 particles remained intact during plastic deformation which was revealed by in-situ 3D X-ray tomography. Hydrogen-induced strain localization at η2 phase interfaces and grain boundaries were inhibited due to strong hydrogen trapping capacity of Al11Mn3Zn2, hence preventing HE cracks initiation. Our approach effectively suppresses hydrogen-induced cracks without sacrificing the ductility, and our strategy can help the design roadmap of HE-tolerant high-strength metallic alloys.

DOI： 10.1016/j.actamat.2022.118110

Repository Public URL： https://hdl.handle.net/2324/6792843

Language：English   Publishing type：Research paper (scientific journal)  

A combination of X-ray nano-tomography and pencil-beam diffraction tomography was utilized for multimodal assessment of the mechanically induced transformation of individual retained austenite grains during tensile deformation in a 0.1C-5Mn-1Si multi-phase steel. In the present study, a newly developed high energy (20 - 30 keV) and high resolution (spatial resolution of 0.16 µm in this study) X-ray nano-tomography technique was applied for the first time to the in-situ observation of a steel under external loading. The gradual transformation, plastic deformation, and rotation behaviour of the individual austenite grains were clearly observed in 3D. It was revealed that the early stage of the transformation was dominated by the stress-assisted transformation that can be associated with measured mechanical driving force, whilst the overall transformation was dominated by the strain-induced transformation that is interrelated with measured dislocation multiplication. The transformation behaviour of individual grains was classified according to their initial crystallographic orientation and size. Noteworthy was the high stability of coarse austenite grains (i.e., 2.5 μm or larger in diameter), contrary to past reports in the literature. Characteristic rotation behaviour and wide data dispersion were also observed in the case of the individual austenite grains. It was conclusively demonstrated that such characteristic behaviour partly originated from interactions with surrounding soft and hard phases. The origins of these characteristics are discussed by combining the image-based and diffraction-based information.

DOI： 10.1016/j.actamat.2022.117956

Repository Public URL： https://hdl.handle.net/2324/6792831

Language：English   Publishing type：Research paper (scientific journal)  

Al-Zn-Mg合金でZn量を１０％まで増やした新奇高強度合金を作製し、その水素脆化挙動をシンクロトロン放射光を用いた超高分解能3D連続観察で明らかにした。この合金の水素脆化挙動を解明すると共に、その防止策も提案した。

DOI： 10.1016/j.actamat.2022.117658

Repository Public URL： https://hdl.handle.net/2324/6792838

Language：English  

Al-Mg合金でMg量を１０％まで増やした新奇高強度合金を作製し、その応力腐食割れ挙動をシンクロトロン放射光を用いた超高分解能3D連続観察で明らかにした。この合金の応力腐食割れ挙動を解明すると共に、その防止策も提案した。

DOI： 10.1016/j.corsci.2021.109343

Repository Public URL： http://hdl.handle.net/2324/4483199

Language：English   Publishing type：Research paper (scientific journal)  

Hydrogen-accelerated spontaneous microcracking in high-strength aluminium alloys
Aluminium alloys are re-evaluated as most feasible way to satisfy the industrial needs of light-weight structural materials. However, unlike conventional structural metals such as iron and titanium, aluminium does not have easily accessible secondary phases, which means that aluminium-based alloys cannot be strengthened by harnessing multiple phases. This leaves age hardening as the only feasible strengthening approach. Highly concentrated precipitates generated by age hardening generally play a dominant role in shaping the mechanical properties of aluminium alloys. In such precipitates, it is commonly believed that the coherent interface between the matrix and precipitate does not contribute to crack initiation and embrittlement. Here, we show that this is not the case. We report an unexpected spontaneous fracture process associated with hydrogen embrittlement. The origin of this quasi-cleavage fracture involves hydrogen partitioning, which we comprehensively investigate through experiment, theory and first-principles calculations. Despite completely coherent interface, we show that the aluminium-precipitate interface is a more preferable trap site than void, dislocation and grain boundary. The cohesivity of the interface deteriorates significantly with increasing occupancy, while hydrogen atoms are stably trapped up to an extremely high occupancy over the possible trap site. Our insights indicate that controlling the hydrogen distribution plays a key role to design further high-strength and high-toughness aluminium alloys.

DOI： 10.1038/s41598-020-58834-6

Language：English   Publishing type：Research paper (scientific journal)  

Assessment of hydrogen embrittlement via image-based techniques in Al-Zn-Mg-Cu aluminum alloys

DOI： 10.1016/j.actamat.2019.06.056

Repository Public URL： http://hdl.handle.net/2324/4149932

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.actamat.2018.08.024

Language：English   Publishing type：Research paper (scientific journal)  

The single-distance phase retrieval technique was applied to contrast-enhanced imaging of the dual phase microstructure of a ferrite/martensite dual-phase with only 1.4% difference in density between the two phases. Each high-resolution absorption-contrast image was registered with a corresponding phase-contrast image, to analyse damage evolution behaviour. The loading step at which each microvoid was nucleated was identified by tracking the microvoid throughout tension, together with its nucleation site. Premature damage initiation was observed at a relatively early stage at various nucleation sites, such as the ferrite interior, martensitic interior and ferrite/martensite interfaces; however, the subsequent growth of such microvoids was relatively moderate. On the other hand, microvoids were also initiated later due to martensitic cracking after the maximum load was reached, and these microvoids subsequently exhibited rapid growth. The martensite cracking induced additional damage evolution mainly along nearby ferrite/martensite interfaces and intersections between the martensite and the ferrite grain boundary. It is notable that the microvoids originating from martensitic cracking exhibited characteristic shear-dominated growth under macroscopic tension, whereas those originating from the other nucleation sites exhibited traditional triaxiality-dominated growth. It was concluded that the ductile fracture was dominated by the substantial force driving the growth of microvoids located on morphologically characteristic martensitic particles. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd.

DOI： 10.1016/j.actamat.2017.01.010

Language：English   Publishing type：Research paper (scientific journal)  

By amalgamating the X-ray diffraction technique with the grain boundary tracking technique, a novel method, diffraction-amalgamated grain boundary tracking (DAGT), has been developed. DAGT is a non-destructive in-situ analysis technique for characterising bulk materials, which can be applied up to near the point of fracture. It provides information about local crystal orientations and detailed grain morphologies in three dimensions, together with high-density strain mapping inside grains. As it obtains the grain morphologies by utilising X-ray imaging instead of X-ray diffraction, which latter is typically vulnerable to plastic deformation, DAGT is a fairly robust technique for analysing plastically deforming materials. Texture evolution and localised deformation behaviours have here been successfully characterised in Al-Cu alloys, during tensile deformation of 27% in applied strain. The characteristic rotation behaviours of grains were identified, and attributed to the effects of interaction with adjacent grains on the basis of the 3D local orientation and plastic strain distributions. It has also been revealed that 3D strain distribution in grains is highly heterogeneous, which is not explained by known mechanisms such as simple incompatibility with adjacent grains or strain percolation through soft grains. It has been clarified that groups consisting of a few adjacent grains may deform coordinately, especially in shear and lateral deformation, and the characteristic deformation pattern is thereby formed on a mesoscopic scale. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2016.01.072

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DOI： 10.2320/matertrans.M2014340

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.2464/jilm.64.557

Language：Japanese   Publishing type：Research paper (scientific journal)  

現在、材料工学、X線光学、計算力学、情報工学の知見を結集した新しい技術体系：リバース4D材料エンジニアリング(R4ME)の提案と創成に関する研究を科研費（基盤研究S）のテーマとして推進している。現在の材料開発は、「材料設計→解析・評価→実材料創出」という時系列で進められているが、R4MEでは、これと逆方向のアプローチにより、迅速かつ高精度に高性能材料を開発するパラダイムチェンジを目指している。現実の材料のマルチスケール3D構造は、その複雑さ故、現在の科学では理論的取り扱いはおろか、そのパターン化さえ困難である。R4MEでは、微視形態を忠実に取り込む高精度4Dイメージベースシミュレーションにより、仮想的にミクロ構造を最適化する。さらに、複雑な3D/4D微視形態を従来の材料設計技術に反映できる程度に粗視化表現することで、ものづくりに展開可能な実用組織制御技術を確立することを目指している。本報は、その中間成果まとめとして著したものである。

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

SPring-8を利用したX線CTを用いれば、結晶粒界にある粒子が鮮明に3D観察できることに着目した。このような粒子は、金属が変形し、破壊していく過程でも常に結晶粒界に位置する為、結晶粒界の粒子の情報を使えば、個々の結晶の形を4Dで求めることができると発想した。2011年度には、この手法を実用的な構造材料に適用できるレベルにまで高精度化することに成功した。この手法により、多結晶材料中のすべての結晶粒の形状の変化を時間を遡りながら4Dで観察することができるようになった。この成果は、金属材料工学では最も権威のある英文誌であるアクタ・マテリアリア誌に掲載が決定された。

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

近年，放射光X線トモグラフィ技術の発達により，現実の材料内部のき裂やひずみの三次元（3D）計側が可能となり，従来は試験断面で行っていた二次元（2D）観察を四次元（4D）観察（時間発展挙動の3D連続観察）に展開でき，材料内部の局所的な力学量を定量化できるようになった。本論文では，X線トモグラフィを用いて，析出状態の異なる7075合金のその場破壊試験を行い，その結果，き裂先端のひずみ分布は，弾塑性破壊力学の規定するものとは大きく異なり，斜め上方および下方の二方向のせん断帯内に大きなひずみが局在化することがわかった。この局在化の程度は，時効状態など従来知られている要因だけでなく，多結晶組織や結晶方位に大きく影響され，負荷の増加とともに局在化の程度が顕著になること，またせん断帯内で相当塑性ひずみに支配される粒子の損傷が生じ，破壊力学が規定する損傷域の10倍以上遠方まで粒子の損傷が生じることを明らかにした。

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.214208

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijhydene.2024.05.146

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2320/matertrans.MT-L2025004

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/21663831.2025.2480165

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.2464/jilm.75.96

Language：English   Publishing type：Research paper (scientific journal)  

Our study investigates how hydrogen trapped at interfaces of MgZn2 precipitates affects hydrogen embrittlement in Al–Zn–Mg alloys. Al–Zn–Mg alloys featuring various aged microstructures were prepared, and their hydrogen embrittlement behaviors were monitored in situ during tensile tests via synchrotron radiation X-ray microtomography. The changes in the interfacial properties of MgZn2 instigated a discernible transition in the quasicleavage and intergranular fractures. First-principles calculations revealed that the hydrogen trapping energy at semicoherent interfaces of MgZn2 is significantly high at 0.56 eV/atom, and multiple hydrogen trapping leads to a substantial reduction in interfacial cohesive energy. Hydrogen partitioning analysis of all trapping sites, including vacancies, grain boundaries, and MgZn2 interfaces, demonstrated that in overaged alloys, more than 90% of the hydrogen was trapped at semicoherent interfaces. The hydrogen trapped at the semicoherent interface of MgZn2 decreased the interfacial cohesive energy, causing semispontaneous decohesion and quasicleavage fracture in the Al–Zn–Mg alloys.

DOI： 10.1016/j.ijhydene.2025.02.123

Repository Public URL： https://hdl.handle.net/2324/7344063

Language：English  

DOI： 10.1016/j.mtcomm.2025.111835

Language：English   Publishing type：Research paper (scientific journal)  

Retrogression and reaging (RRA) treatment is a distinctive approach to counteract hydrogen embrittlement in 7xxx Al alloys without compromising strength. However, the mechanistic understanding of RRA has long centered around grain-boundary-related phenomena, while the roles of grain-interior microstructures in hydrogen embrittlement have remained unclear. Here, we demonstrate the beneficial effect of RRA in reducing transgranular cracks in a specially selected high-Zn alloy that exhibits fully quasi-cleavage cracking, thereby enabling the precise decoupling of grain-interior and grain-boundary mechanisms. Using synchrotron radiation 3D observations, we identify a significant delay in the initiation of transgranular cracks in RRA-treated specimens as compared to those in the peak-aged condition. Atomic-resolution electron microscopy observations confirm the grain-interior partial transformation from the coherent η’ phase to the semi-coherent η phase. It is proposed that the increased fraction of semi-coherent η/Al interfaces reduces hydrogen coverage at coherent interfaces, thereby suppressing transgranular hydrogen-induced debonding on the slip planes.

DOI： 10.1016/j.scriptamat.2024.116383

Repository Public URL： https://hdl.handle.net/2324/7327006

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jallcom.2024.177781

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijhydene.2024.11.265

Repository Public URL： https://hdl.handle.net/2324/7344062

Language：English   Publishing type：Research paper (scientific journal)  

Ultrastrong metallic alloys, possessing unparalleled load-bearing abilities, are coveted in many sectors, thus attracting growing research efforts. However, these alloys encounter persistent usability challenges posed by hydrogen embrittlement, which causes unpredictable fracture through crack initiation. Due to complex hydrogen-microstructure interactions and their exacerbation under high stress, advances in hydrogen resistance in ultrastrong materials are sparse throughout their long history. Herein, we report a quantum-mechanics-informed strategy for hydrogen tolerance enhancement in ultrafine-grain-hardened Al-Zn-Mg-Cu alloys, approaching their current strength limit of approximately 1 GPa. This method involves the incorporation of hydrogen-absorbing T-phase precipitates into nanograins, to substantially reduce hydrogen coverage at potential crack initiation sites. We demonstrate, via synchrotron radiation X-ray micro-/nano-tomography, scanning transmission electron microscopy and atom probe tomography, that nanoprecipitates successfully withstand shear strains exceeding 1000 and are exploitable essentials for ultra strength-hydrogen synergy, contrasting their often-assumed secondary roles in nanocrystalline alloys due to possible strain-induced dissolution, which has intuitively excluded exploring them as central elements. Our approach potentially inspires new hydrogen-resisting alloys across a broad strength-composition space.

DOI： 10.1016/j.corsci.2024.112471

Repository Public URL： https://hdl.handle.net/2324/7327005

Language：English   Publishing type：Research paper (scientific journal)  

The internal microstructures of Ni–P-plated Al–Zn–Mg-based alloys were investigated using synchrotron X-ray computed tomography, together with various analytical methods for hydrogen detection. We clarified that hydrogen-induced pores were generated and segregated near the top and bottom surfaces of a rolled sheet of a commercial-purity Al–Zn–Mg-based alloy with Ni–P plating. In contrast, such segregation of hydrogen micropores was not observed in the high-purity-grade Al–Zn–Mg alloys with Ni–P plating. This result suggests that hydrogen enters the Ni–P plating layer during the plating operation and generates pores in the surface region owing to surface inclusions. Additionally, the hydrogen-induced defects deteriorated the tensile properties such as tensile strength and elongation of the commercial-purity Al–Zn–Mg-based alloys containing higher levels of impurities such as Fe and Si with Ni–P plating.

DOI： 10.1016/j.ijhydene.2024.07.380

Language：English   Publishing type：Research paper (scientific journal)  

In Al-Zn-Mg alloy, hydrogen (H) leads remarkably to the degradation of mechanical properties. It is indispensable to suppress this phenomenon called hydrogen embrittlement (HE) for developing the high-strength Al-Zn-Mg alloy. Because intergranular fracture (IGF) is mainly observed when HE occurs in the alloy, we need to understand the initiation behavior of IGF in order to suppress HE. Heterogeneous distribution of stress, strain and H concentration usually influence the IGF initiation in polycrystalline material. In the present study, we investigated distribution of stress, strain, and H concentration in actual fractured regions by simulation employing a crystal plasticity finite element method and H diffusion analysis in a 3D image-based model, which was created based on 3D polycrystalline microstructure data obtained from X-ray imaging technique. Combining the simulation and in-situ observation of the tensile test sample by X-ray CT, we examined the distribution of stress, strain, and H concentration in actual crack initiation behavior. Based on this, the condition for intergranular crack initiation were discussed. As a result, it is revealed that stress normal to grain boundary induced by crystal plasticity dominates intergranular crack initiation. In contrast, accumulation of internal H due to the stress has little impact on crack initiation.

DOI： 10.2320/matertrans.MT-L2024007

Repository Public URL： https://hdl.handle.net/2324/7234369

Language：English   Publishing type：Research paper (scientific journal)  

Excellent strength–ductility balance in metastable Fe–Cr–Ni austenitic alloys stems from phase transformation from austenite (fcc structure) to αʹ martensite (bcc structure) during deformation, namely deformation-induced αʹ martensitic transformation (DIMT). Here, DIMT in a metastable Fe–17Cr–7Ni austenitic alloy was detected in situ and characterized in three dimensions (3D) by employing synchrotron radiation X-ray microtomography. This technique utilizes refraction contrast, which is attributable to the presence of phase boundaries between the parent austenite and the newly formed αʹ martensite phase. By combining microtomography and position-sensitive X-ray diffraction, we succeeded in crystallographically identifying multiple αʹ martensite phases continuously transformed in four groups from a single parent austenitic phase.

DOI： 10.1038/s41598-024-65505-3

Language：English   Publishing type：Research paper (scientific journal)  

This study aims to clarify the growth process of the β-phase in Al-Mg-Si alloys from the point of view of morphological evolution. The orientation relationship, shape, growth process, misfit value, and interfacial condition between the β-phase and Al matrix were investigated using high-resolution transmission electron microscopy (HR-TEM), focused ion beam (FIB), and optical microscope (OM). In a previous study, the growth process and shape of the β-phase were determined using scanning electron microscopy (SEM). It was proposed that the truncated octahedron (8{111}, 6{100} facets) transforms into a hexahedron (6{100} facets). This study proposes that two new three-dimensional shapes of the β-phase exist between the truncated octahedron and hexahedron, and we identified the {111}β facets at the edges of the β-phase. We proposed the morphology evolution during the growth process of Mg2Si crystals and calculated the misfit to understand that the unstable {111}β facet has a higher misfit value compared to the {001}β and {011}β facets. Our observations provide insight into how they influence the behavior of Mg2Si crystals, which is crucial for predicting the microstructural evolution of Al-Mg-Si alloys and for designing materials with desired properties.

DOI： 10.1016/j.jallcom.2024.174234

Language：English   Publishing type：Research paper (scientific journal)  

In order to observe type IV fracture occurring in the HAZ fine-grained zone of a modified 9Cr–1Mo steel at high resolution, the creep damage process of a single notched specimen was continuously observed in three dimensions. The initiation, growth and coalescence behaviour of individual creep voids were clearly observed. This was combined with an analysis of the local stress state using the finite element method. Furthermore, all creep voids that could be observed in the final loading stage were traced backward in time to determine the loading stages at which the creep voids were initiated together with the growth behaviour of the individual creep voids. Significant creep void formation was observed a little further in from the bottom of the notch, where the maximum principal and hydrostatic stresses were greatest, while the stress triaxiality was greatest a little closer to the centre of the specimen than the maximum principal and hydrostatic stresses, where significant creep void growth was observed. It was found that the creep voids nucleated at an early loading stage dominated the creep failure of the specimen. The growth behaviour could be well approximated by the model that combined the diffusion law and power creep law with the constraint effect from neighbouring grains. Engineering parameters that describe the progress of type IV damage were also investigated.

DOI： 10.1016/j.msea.2024.146607

Repository Public URL： https://hdl.handle.net/2324/7237116

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Recent research has shown that some intermetallic compound particles with high interfacial hydrogen trap energies (e.g., Mg2Si) are prone to damage at high hydrogen concentrations. In this study, the acceleration of particle damage in an A6061 alloy was observed in-situ via X-ray CT. The damage behavior of the particles that are located in the crack tip stress field, where high stress triaxiality causes a local increase in the hydrogen concentration, was analyzed. The influence of hydrogen on the damage behavior of the dispersed Mg2Si particles was investigated by preparing a material charged with hydrogen to achieve extremely high hydrogen concentration, and further hydrogen enrichment in a crack tip region was also utilized. Interfacial debonding of Mg2Si particles was frequently observed in the vicinity of a crack tip immediately prior to tensile fracture. Even though the fracture is typical of ductile fracture, hydrogen accelerates particle damage and reduces the macroscopic ductility of the aluminum alloy. This can be considered as a form of hydrogen embrittlement of aluminum alloys. Even in materials with relatively low hydrogen concentrations (0.85 mass ppm), interfacial debonding occurred in the hydrogen-enriched crack tip regions. A higher hydrogen concentration promoted interfacial debonding over a wider range of particle sizes and particle shapes. It can be inferred that localized hydrogen enrichment, which is expected to occur due to external hydrogen exposure, stress corrosion cracking, corrosion or crack tips, can directly contribute to debonding at the Mg2Si particle/aluminum matrix interface. According to the analysis, reduction of the diameter and simplification of the shape of Mg2Si particles are effective method for suppressing such hydrogen-induced debonding.

DOI： 10.2320/matertrans.MT-M2024026

Repository Public URL： https://hdl.handle.net/2324/7234367

Language：English   Publishing type：Research paper (scientific journal)  

Hydrogen at the mass ppm level causes hydrogen embrittlement in metallic materials, but experimentally elucidating the hydrogen trapping sites is extremely difficult. We exploit the fact that positive muons can act as light isotopes of hydrogen to study the trapping state of hydrogen in matter. Zero-field muon spin relaxation experiments and density functional theory (DFT) calculations of the hydrogen trapping energy are carried out for Al6Mn. The DFT calculations reveal four possible trapping sites for hydrogen in Al6Mn, at which the hydrogen trapping energies are 0.168 (site 1), 0.312 (site 2), 0.364 (site 3), and 0.495 (site 4) in units of eV/atom. The variations in the deduced dipole field width (Δ) with temperature indicate noticeable changes at 94, 193, and 236 K. Considering the site densities, the observed Δ change temperatures are interpreted as muon trapping at sites 1, 3, and 4.

DOI： 10.1016/j.scriptamat.2024.116051

Repository Public URL： https://hdl.handle.net/2324/7234036

Language：English   Publishing type：Research paper (scientific journal)  

Surrogate-based microstructural optimization was applied to model the relationship between local crystallographic microstructure and intergranular hydrogen embrittlement in an Al–Zn–Mg alloy, and a support vector machine with an infill sampling criterion was used to realise high-accuracy optimisation with a limited data set. This methodology integrates thoroughgoing microstructural quantification, two coarsening processes, and surrogate modelling. An objective function was defined together with 66 design parameters that quantitatively express size, shape, orientation and damage during specimen machining for surface grain boundaries and grains. The number of design parameters was then reduced from 66 to 3 during the two-step coarsening process. It has been clarified that intergranular crack initiation can be described using the simple size of grains and grain boundaries together with grain boundary orientation with respect to the loading direction. It can be inferred that these design parameters are of crucial importance in crack initiation through elevation in stress normal to grain boundaries. Correlation between the selected design parameters and crack initiation was somewhat weak compared to past applications of a similar technique to particle damage. The reason for this is discussed. The present approach offers a cost-efficient solution for the prevention of hydrogen embrittlement through 3D design of crystallographic microstructure that cannot be obtained using conventional strategies for developing materials.

DOI： 10.2320/matertrans.MT-M2023116

Repository Public URL： https://hdl.handle.net/2324/7160864

Language：Japanese   Publishing type：Research paper (scientific journal)  

In Al-Zn-Mg alloy, hydrogen leads to degradation of mechanical properties. It is indispensable to suppress this phenomenon called hydrogen embrittlement (HE) for increasing the strength of Al-Zn-Mg alloy. Intergranular fracture (IGF) mainly occurs when HE affects this alloy. In order to suppress HE, we need to understand the initiation behavior of IGF. Heterogeneous distribution of stress, strain and hydrogen concentration in polycrystalline material have an influence on the IGF initiation. In the present study, distribution of stress, strain and hydrogen concentration in actual fractured regions were investigated by employing a crystal plasticity finite element method and hydrogen diffusion analysis using a 3D-image-based model. This model was created based on 3D polycrystalline microstructure data obtained from X-ray imaging technique. By combining in-situ observation of tensile test of the same sample by X-ray CT with the simulation, we compared distribution of stress, strain and hydrogen concentration with actual crack initiation behavior. Based on this, the condition for intergranular crack initiation were discussed. As a result, it is revealed that stress load perpendicular to grain boundary induced by crystal plasticity dominate intergranular crack initiation. In addition, accumulation of internal hydrogen induced by crystal plasticity had little impact on crack initiation.

DOI： 10.2464/jilm.73.530

Repository Public URL： https://hdl.handle.net/2324/7162034

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5006/4300

Repository Public URL： https://hdl.handle.net/2324/7160861

Language：Japanese   Publishing type：Research paper (scientific journal)  

An increase in the volume fraction of pores in aluminum alloys causes a decrease in the elongation and the strength of alloys. To improve the mechanical properties of aluminum alloys, it is important to understand the growth and shrinkage behavior of pores. In this study, we analyzed the relationship between hydrogen desorption behavior and the growth/shrinking behavior of pores in A6061 alloys and pure aluminum using thermal desorption analysis and synchrotron radiation X-ray tomography. In pure aluminum, the fine pores began to annihilate at temperatures above 500°C and the relatively large pores coarsened. In contrast, the pores shrank with increasing temperature in A6061 alloy. The influence of second-phase particles has been discussed as a possible explanation for the difference in the nature of pores at elevated temperatures in pure aluminum and A6061 alloys. As in the A6061 alloy, much of the hydrogen desorbed from the pores due to heating is released externally from the second-phase particles on the aluminum surface, resulting in pore shrinkage due to the internal pressure drop of pores.

DOI： 10.2464/jilm.73.212

Language：English   Publishing type：Research paper (scientific journal)  

Although hydrogen embrittlement susceptibility of high-strength Al alloys is recognized as a critical issue in the practical use of Al alloys, identifying the hydrogen trapping or distribution has been challenging. In the present study, an effective approach based on experiment and simulation is proposed to explore the potential trap sites in Al alloys. At first, zero-field muon spin relaxation experiments were implemented in the temperature range from 5 K to 300 K. The plot of the temperature dependence of dipole field widths (∆) provides several characteristic peaks corresponding to the hydrogen trapping. Four dilute Al alloys (Al–Mg, Al–Cu, Al–Ti, and Al–V) were chosen to explore the possible trap sites. Atomic configurations of the muon trapping sites corresponding to the observed ∆ peaks are well assigned using the first-principles calculations for the binding energies of hydrogen around a solute and solute-vacancy pair. The extracted linear relationship between the muon ∆ peak temperature and the binding energy enables us to explore the potential alloying elements and their complex that have strong binding energies with hydrogen in Al alloys.

DOI： 10.1007/s11661-023-07024-w

Language：English   Publishing type：Research paper (scientific journal)  

Local 3D short fatigue crack closure behavior was investigated in Ti-6Al-4V alloy using ultra-high-resolution X-ray microtomography (XMT). The results show that the inhomogeneous distribution of plasticity-induced and roughness-induced crack closure is caused by the variation of crack path morphologies. These crack path morphologies exhibited heterogeneous plastic deformation at the crack-tips due to the anisotropic nature of α grains and varying extents of crack tilting and twisting caused by the interaction of the crack front with α/α boundary or α/α + β interface. It was revealed via surrogate-based statistical analysis that the Schmid factor has the strongest effect on crack growth rate.

DOI： 10.1016/j.ijfatigue.2022.107428

Repository Public URL： https://hdl.handle.net/2324/7153597

Language：English   Publishing type：Research paper (scientific journal)  

The hexagonal tabular ß-Mg2Si phase (hex-ß) co-existed with conventional truncated octagonal shaped ß-Mg2Si (con-ß) in Al-1.0 mass% Mg2Si alloy containing a small amount of noble metal elements (NMEs; Cu, Pt, Ag, Pd or Au) at the over-aged condition of 673 K. As this hex-ß laid on the {111} plane of the Al matrix, and its six edges were parallel to <110>ß, its orientation relationship with the Al-matrix is as follows:{111Al //{111}ß and <110>Al //<110>β was the same as our previous report of (hex-ß) in an ingot of Al-1.0 mass%Mg2Si- 0.5 mass% Cu alloy just homogenized at 723 K for 4 days, without cold-rolling, solution heat treatment, and aging. There is no significant difference in the lattice parameter of ß-Mg2Si by added NMEs. The formation of hex-ß was suggested to be related to defects in the Al-matrix, for example, by segregation of NMEs at the interface, altering the stacking fault energy, or introducing partial dislocations.

DOI： 10.1016/j.mtcomm.2023.106198

Language：English   Publishing type：Research paper (scientific journal)  

Recent studies have revealed that hydrogen embrittlement in Al-Zn-Mg alloys appears to be dominated by hydrogen partitioning to MgZn2 precipitates. A method has recently been proposed for reducing the hydrogen concentration at MgZn2 precipitates by adding specific intermetallic compound particles that have high hydrogen trap energy. In the present study, the effectiveness of Al7Cu2Fe particles on suppression of hydrogen embrittlement in Al-Zn-Mg-Cu alloys was evaluated using X-ray microtomography. Quasi-cleavage cracks were found to be initiated in regions where local volume fractions of the Al7Cu2Fe particles were relatively low. Hydrogen partitioning to the MgZn2 precipitate interface was suppressed, even in high hydrogen concentration material, by adding Al7Cu2Fe particles. However, the fractional area of the quasi-cleavage fracture in the material with high hydrogen concentration was higher due to insufficient hydrogen diffusion inside the Al7Cu2Fe particles and at the interface between the aluminum matrix and the particles. It appears that finely distributed small Al7Cu2Fe particles might effectively suppress hydrogen embrittlement.

DOI： 10.2320/matertrans.MT-L2022007

Repository Public URL： https://hdl.handle.net/2324/7153596

Language：English   Publishing type：Research paper (scientific journal)  

In recent years, it has been reported that intermetallic compound particles can suppress hydrogen embrittlement by hydrogen trapping. Some intermetallic particles in aluminum alloys, such as Al7Cu2Fe, have internal hydrogen trap sites; it is proposed that hydrogen embrittlement can be suppressed by preferential hydrogen partitioning in these sites. However, intermetallic compound particles act as fracture origin sites, and excessive addition degrades the mechanical properties of the material. In this study, we quantitatively evaluated the damage and decohesion behavior of intermetallic compound particles in high-hydrogen content 7XXX aluminum alloys by using in situ synchrotron radiation X-ray tomography. The results revealed that the hydrogen particles induced early high-strain localization, and the Al7Cu2Fe particles were damaged in that region due to its brittleness, resulting in early fracture. Hydrogen had no effects on the fracture and debonding behaviors of intermetallic compound particles, suggesting that the observed particle brittle fracture is dependent on their mechanical properties.

DOI： 10.2320/matertrans.MT-L2022020

Language：Japanese   Publishing type：Research paper (scientific journal)  

In recent years, it has been reported that intermetallic compound particles can suppress hydrogen embrittlement by hydrogen trapping into them. Some intermetallic particles in aluminum alloys, such as Al7Cu2Fe, have internal hydrogen trap sites and it is proposed that hydrogen embrittlement can be suppressed by preferential hydrogen partitioning to these sites. However, intermetallic compound particles act as fracture origin, and excessive addition degrades the mechanical properties. In this study, we quantitatively evaluated the damage and decohesion behavior of intermetallic compound particles in high-hydrogen 7XXX aluminum alloys by using in-situ synchrotron radiation X-ray tomography. As the results, it has been revealed that hydrogen induced early high-strain localization, and the Al7Cu2Fe particles were damaged in that region due to own brittleness, resulting in early fracture. Hydrogen had no effect on the fracture and debonding behavior of intermetallic compound particles, suggesting that observed brittle fracture of particles is dependent on the mechanical properties of the particles.

DOI： 10.2464/jilm.72.411

Language：English   Publishing type：Research paper (scientific journal)  

Crystallographic assessment of the hydrogen embrittlement behavior of AlZnMg alloy was performed by means of a technique combining fracture trajectory analysis and synchrotron X-ray diffraction contrast tomography. The 3D microstructure reconstructed using diffraction contrast tomography contained 119 grains. Fracture surfaces revealing intergranular fracture, ductile fracture, and quasi-cleavage fracture were observed in the alloy. While the intergranular crack initiated at a grain boundary with high grain boundary energy and a high angle between the grain boundary plane and loading direction, the crack propagation itself was not observed to be sensitive to these two parameters. The quasi-cleavage fracture surfaces were not characterized by any specific crystal orientation because of variation in the free surface segregation energy of hydrogen uniforms without depending on surface orientation.

DOI： 10.2320/matertrans.MT-L2021020

Repository Public URL： https://hdl.handle.net/2324/7153598

Language：English   Publishing type：Research paper (scientific journal)  

This paper is associated with a larger program of research, studying the resistance to hydrogen-induced stress cracking (HISC) of a wrought and a hot isostatically pressed UNS S31803 duplex stainless steel (DSS), with respect to both the independent and interactive effects of the three key components of HISC: microstructure, stress/strain, and hydrogen. In the first part presented here, several material properties such as the three-dimensional microstructure, distribution, and morphology/geometry of the two phases, i.e., ferrite and austenite, and their significance on hydrogen transport have been determined quantitatively, using x-ray computed tomography microstructural data analysis and modeling. This provided a foundation for the study to compare resistance to HISC initiation and propagation of the two DSSs with differing microstructures, using hydrogen permeation measurements, environmental fracture toughness testing of single-edge notched bend test specimens, in Part 2 paper of this study (Blanchard, et al., Corrosion 78, 3 [2022]: p. 258-265).

DOI： 10.5006/3960

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.18957/rr.10.1.51

Language：Japanese   Publishing type：Research paper (scientific journal)  

CT Observation and Finite Element Analysis for Fatigue Crack Initiation in Cast Aluminum Alloy

Language：Japanese  

In-situ synchrotron X-ray microtomography has been employed to investigate the three-dimensional (3D) closure behavior of short fatigue crack in Ti-6Al-4V alloy. At a spatial resolution level of 1 µm, tomography datasets were taken at two short crack fronts to observe the time evolution behavior of closure (sometimes called 4D imaging). Owing to the high spatial resolution level, the complex 3D crack morphology consisting of deflections, facet paths and crack branching/overlap caused by the 3D variation in the microstructural features were readily observed together with the occurrence of crack closure. This study separated the contributions of near-tip and behind-tip crack closure and observed their behavior with crack growth. It was deduced that the evolution of behind-tip closure with increase in crack length predominantly affects the overall closure behavior in the short crack regime. Crack front closure behavior variation was found to be attributable to the existence of different crack path morphologies which showed varied degree of fracture surface roughness due to Mode II and Mode III displacements. The relationship between closure, crack tip opening displacement range (ΔCTOD) and crack growth rate are also discussed.

DOI： 10.1016/j.engfracmech.2021.107755

Repository Public URL： http://hdl.handle.net/2324/4483403

Language：English   Publishing type：Research paper (scientific journal)  

Hydrogen embrittlement in aluminum alloys occurs due to local hydrogen accumulation during deformation. Investigating hydrogen diffusion with plastic deformation can help researchers further understand hydrogen embrittlement behavior in terms of its occurrence condition. We assessed hydrogen accumulation behavior in AlZnMg alloys under strain by combining tensile testing with Kelvin force microscopy. Additionally, the effects of microstructures on hydrogen accumulation were analyzed in detail. Hydrogen accumulated around specific grain boundaries, and it was likely that accumulated hydrogen was repartitioned to the generated vacancies, due to deformation, and the precipitate interfaces.

DOI： 10.2320/matertrans.l-m2020873

Repository Public URL： http://hdl.handle.net/2324/4485353

Language：English  

Crack initiation and early propagation behavior of the directionally solidified (DS) superalloy CM247LC has been assessed by data rich imaging approaches. These include conventional characterization methods such as replica record analysis, 3D optical surface imaging, optical and scanning electron microscopy (SEM) as well as more recent techniques like digital image correlation (DIC) and synchrotron radiation computed tomography (SRCT). Three modes of secondary crack behaviors were found during evaluation of the fatigue process. The early stages of fatigue damage were controlled by microstructure-induced cracking, mainly consisting of carbide cracking. Fatigue damage was then promoted via slip band cracking and opening mode controlled carbide-cracking. The mechanisms of these different cracking behaviors are associated with the plastic zone of the main crack tip. Even though the early localized strain levels were of the same intensity within slip bands and at the intersection sites with carbides, carbide-induced cracking occurred prior to slip band cracking, characterized by SEM-DIC. This indicated that carbide-induced cracking was more likely to occur in the early stages of the fatigue process. Early crack growth behaviors were further investigated in situ at the microstructural scale via SRCT. The effect of carbides on crack initiation and propagation processes were evaluated in 3D. This revealed the phenomenon around pores, that cracks simultaneously grew on different slip planes in 3D, contrary to previous theories that such cracks tend to grow on a single favourable slip plane (in polycrystalline alloys). The SRCT result demonstrates the importance and necessity of 3D characterization of the crack propagation behavior at sub-surface, which is not fully analyzed by 2D characterization.

DOI： 10.1016/j.msea.2020.140592

Language：English  

In this study, high-energy x-ray nanotomography (nano-computed tomography, nano-CT) based on full-field x-ray microscopy was developed. Fine two-dimensional and three-dimensional (3D) structures with linewidths of 75 nm-100 nm were successfully resolved in the x-ray energy range of 15 keV-37.7 keV. The effective field of view was ∼60 μm, and the typical measurement time for one tomographic scan was 30 min-60 min. The optical system was established at the 250-m-long beamline 20XU of SPring-8 to realize greater than 100× magnification images. An apodization Fresnel zone plate (A-FZP), specifically developed for high-energy x-ray imaging, was used as the objective lens. The design of the A-FZP for high-energy imaging is discussed, and its diffraction efficiency distribution is evaluated. The spatial resolutions of this system at energies of 15 keV, 20 keV, 30 keV, and 37.7 keV were examined using a test object, and the measured values are shown to be in good agreement with theoretical values. High-energy x-ray nano-CT in combination with x-ray micro-CT is applied for 3D multiscale imaging. The entire bodies of bulky samples, ∼1 mm in diameter, were measured with the micro-CT, and the nano-CT was used for nondestructive observation of regions of interest. Examples of multiscale CT measurements involving carbon steel, mouse bones, and a meteorite are discussed.

DOI： 10.1063/5.0020293

Language：English  

Hydrogen Trapping in Mg2Si and Al7FeCu2 Intermetallic Compounds in Aluminum Alloy: First-Principles Calculations
<p>From first-principles calculations, we estimated the trapping energy of hydrogen atom at the interstitial site of perfect crystals of Mg₂Si and Al₇FeCu₂ intermetallic compounds in the aluminum matrix. We found that Al₇FeCu₂ trapped hydrogen atoms strongly, whereas Mg₂Si did not. The highest trapping energy in Al₇FeCu₂ is 0.56 eV/atom. We also found that the density of hydrogen trapping can be increased up to about 13 atoms/nm³ while keeping high trapping energy of about 0.40 eV/atom. We inferred that the Al₇FeCu₂ phase might remove hydrogen from the aluminum matrix, hence, preventing hydrogen embrittlement of aluminum alloy.</p>

DOI： 10.2320/matertrans.MT-M2020201

Language：English   Publishing type：Research paper (scientific journal)  

Metastable phases in aluminium alloys are the primary nano-scale precipitates which have the biggest contribution to the increase in the tangible mechanical properties. The continuous increase in hardness in the 7xxx aluminium alloys is associated with the phase transformation from clusters or GP-zones to the metastable eta ' phase. The high-resolution electron imaging is used to observe the precipitates and reconstruct a kinetic model that might explain the transformation. This work is an attempt to gain insight into how the structural transformation may occur based on the shortest route of diffusion for the eventual structure to result in that of the eta ' phase.

DOI： 10.1080/02670836.2020.1821323

Language：English   Publishing type：Research paper (scientific journal)  

The nucleation, growth, and coalescence of microvoids are examined in high Zn and Mn content 7XXX aluminum alloys using high-resolution synchrotron X-ray microtomography. The results have clearly shown that the addition of Mn content (0.6% mass) increases the ultimate tensile strength with limited ductility. The loading step in which each microvoid was nucleated together with its nucleation site is determined by tracking the microvoids in reverse chronological order from the final loading step towards the initial stress-free loading step. It was observed that microvoids were initiated due to particle cracking, and void nucleation occurs continuously with the applied strain. Furthermore, it was also observed that the particle underwent multiple fractures. It was concluded the ductile fracture was dominated by the nucleation and growth of microvoids due to particle fracture.

DOI： 10.1016/j.msea.2020.139423

Language：Japanese   Publishing type：Research paper (scientific journal)  

Analysis of Hydrogen Content in Pure Palladium via Neutron Radiography and Tomography

DOI： 10.2320/jinstmet.J2020017

Repository Public URL： http://hdl.handle.net/2324/4485350

Language：English  

DOI： 10.4028/www.scientific.net/AMR.794.476

Language：English   Publishing type：Research paper (scientific journal)  

Al–Zn–Mg alloys are representative high-strength aluminum alloys, but hydrogen embrittlement hinders further strengthening. The role of nanovoids in the hydrogen embrittlement of a hydrogen-charged Al–Zn–Mg–Cu alloy is examined using high-resolution imaging-type synchrotron X-ray tomography. Although nanovoids are initiated during deformation, their growth and coalescence behaviors are limited. Hydrogen partitioning analysis indicates that this is because most of the formed vacancies are not stabilized because of the low hydrogen occupancy. Furthermore, 3D/4D clustering analyses of nanovoids reveal that they do not aggregate on a specific plane to initiate a crack, and that linkage between nanovoids is less likely to occur.

DOI： 10.1016/j.mtla.2020.100667

Repository Public URL： http://hdl.handle.net/2324/4485341

Language：English   Publishing type：Research paper (scientific journal)  

An unreported precipitate orientation relationship in Al-Zn-Mg based alloys

DOI： 10.1016/j.matchar.2019.109958

Language：Japanese   Publishing type：Research paper (scientific journal)  

Neutron Imaging Analysis of Hydrogen Content in Pure Palladium and Aluminum Alloys
<p>The visualization of hydrogen distribution in materials is important to understand hydrogen embrittlement behavior. Neutron imaging experiment was carried out in order to visualize the distribution of solute hydrogen in an Al-10.1％Zn-1.2％Mg alloy and a pure palladium after hydrogen charging. Changes in the contrast of neutron transmission images caused by hydrogen were clearly observed in a palladium. In the wavelength range of 2-3 Å and 5-13.5 Å, the mean neutron transmission around the center of a hydrogen-charged palladium were 0.692 and 0.511, respectively. The hydrogen content in a palladium was estimated to be 10.8 mol％ from the measured neutron transmission. In this study, it has been demonstrated that hydrogen content can be analyzed even in non-monochromatic neutron imaging by considering the wavelength dependence of neutron intensity, and the effects of incoherent scattering and of Bragg-edge on transmission. On the other hand, hydrogen could not be observed from the neutron transmission image in Al-Zn-Mg alloys. This was due to the low hydrogen content, which was mass ppm level even after hydrogen charging, and statistical precision was not sufficient to discuss the amount of hydrogen of the mass ppm order.</p>

DOI： 10.2320/jinstmet.J2019016

Repository Public URL： http://hdl.handle.net/2324/4355441

Language：English   Publishing type：Research paper (scientific journal)  

Effects of 3D microstructural distribution on short crack growth behavior in two bimodal Ti-6Al-4V alloys

DOI： 10.1016/j.msea.2019.138264

Repository Public URL： http://hdl.handle.net/2324/4150459

Language：Japanese   Publishing type：Research paper (scientific journal)  

Quantitative evaluation of creep voids in Mod.9Cr-1Mo steel welded joints with X - Ray micro-tomography
© 2019 The Society of Materials Science, Japan. High-chromium ferritic resisting steels have been commonly used for high temperature components of USC boilers. However, it is well known that in the welded joints TYPE IV damage occurs in the fine-grained HAZ during long-term use under elevated temperature, due to the multiaxial stress at the fine-grained HAZ region. TYPE IV damage develops by the creep void nucleation at grain boundaries, following the void growth and coalescence. In order to measure the amount of creep damage, the distribution of voids on two-dimensional cross section is normally observed. However, the damage evaluation has a limitation from the point of accuracy because the void grows three-dimensionally. Recently, X-ray CT has been applied to observe damage distribution in three dimensions, and it is known that X-ray μ-CT in SPring-8, which is synchrotron radiation facility, can detect a void of about 1 μm diameter. In this paper, the TYPE IV damage is observed with X-ray μ-CT. The amount of void nucleation and the size of voids in the fine-grained HAZ region with time are quantitatively evaluated. Comparison between the creep damage evaluations based on two dimensional cross section (average diameter, area fraction and number density) and three dimensional void observations is conducted. It appears that the evaluation based on the area fraction on cross section is closest to that in three dimensions and therefore the most suitable evaluation.

DOI： 10.2472/jsms.68.599

Repository Public URL： http://hdl.handle.net/2324/4123952

Language：English   Publishing type：Research paper (scientific journal)  

Characterisation of structural similarities of precipitates in Mg-Zn and Al-Zn-Mg alloys systems

DOI： 10.1080/14786435.2019.1637032

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.engfracmech.2019.106503

Repository Public URL： http://hdl.handle.net/2324/4483200

Language：English   Publishing type：Research paper (scientific journal)  

Local Deformation and Fracture Behavior of High-Strength Aluminum Alloys Under Hydrogen Influence

DOI： 10.1007/s11661-019-05304-y

Repository Public URL： http://hdl.handle.net/2324/4483196

Language：English   Publishing type：Research paper (other academic)  

4D characterization of the stress corrosion cracking behavior in Al-10Mg aluminium alloy via synchrotron X-ray tomography

Language：English   Publishing type：Research paper (scientific journal)  

Effect of Copper Addition on Precipitation Behavior near Grain Boundary in AlZnMg Alloy

DOI： 10.2320/matertrans.L-M2019828

Language：Japanese   Publishing type：Research paper (scientific journal)  

Influence of hydrogen on stress corrosion cracking behavior in Al-10Mg alloy
© 2019 The Japan Institute of Light Metals It is known that the susceptibility to stress corrosion cracking of Al-Mg alloy increase with increasing Mg content, whereas the strength of Al-10Mg alloy reach to that of 2000 and 7000 series Al alloys. In-situ observation of the stress corrosion cracking of a hydrogen charged Al-10Mg alloy was conducted by using synchrotron X-ray mi-crotomography in SPring-8. The corrosion area and crack were observed in hydrogen charged material with water atmosphere. The corrosion and crack grow up with increasing applied strain. In addition, deformation localization and high hydrostatic strain that was caused by nucleation of nanovoids during deformation was also observed in crack tip. These observations indicated that the stress corrosion cracking of an Al-10Mg alloy occurs due to the influence of hydrogen.

DOI： 10.2464/jilm.69.223

Language：Japanese   Publishing type：Research paper (scientific journal)  

Hydrogen desorption behavior in Al-8&#37;Zn-1&#37;Mg alloy
© 2019 The Japan Institute of Light Metals The increase in Zn or Mg content results in an increase in Al-Zn-Mg alloys strength, however they become more susceptible to hydrogen embrittlement. To understand the hydrogen embrittlement behavior, it is necessary to study the hydrogen trapping behavior. In the present study, Al-8&#37;Zn-1&#37;Mg was made in order to have six trap sites (vacancies, dislocations, grain boundaries, particles, precipitates and micropores) and hydrogen trapping behavior in those trap sites was assessed by means of thermal desorption analysis (TDA). In addition, micropores were evaluated in detail using X-ray microtomography. Hydrogen desorption energies from grain boundaries and micropores were calculated using TDA curves. These values were 2 to 3 times larger than the ones reported in the literature due to a change in the trap sites during thermal desorption test. Increase in the number density of micropores was observed above 673 K during thermal desorption experiment. As the temperature increases, it has been reasonably inferred that some hydrogen desorbed from trap sites are released from the specimen and the rest of hydrogen is redistributed to form new micropores. It is revealed that low heating rate induces a change in trap sites and affect the measurement of hydrogen desorption energies.

DOI： 10.2464/jilm.69.186

Language：English   Publishing type：Research paper (scientific journal)  

Assessment of predominant microstructural features controlling 3D short crack growth behavior via a surrogate approach in Ti-6Al-4V

DOI： 10.1016/j.msea.2019.01.116

Repository Public URL： http://hdl.handle.net/2324/4150458

Language：English   Publishing type：Research paper (scientific journal)  

Abnormally enhanced diamagnetism in Al-Zn-Mg alloys
Temperature and time dependences of magnetization of Al-1.0&#37;Zn-4.2&#37;Mg, Al-2.6&#37;Zn-3.2&#37;Mg, Al-4.1&#37; Zn-1.1&#37;Mg, and Al-5&#37;Zn (at.&#37;) alloys were measured in the range between 10 and 310 K after various periods of natural aging and peak-aged heat treatments. Enhanced diamagnetic contributions on the magnetization were observed for the as-quenched Al-Zn-Mg alloys for the first time. The enhanced diamagnetism observed in Al-2.6&#37;Zn-3.2&#37;Mg and Al-4.1&#37;Zn-1.1&#37;Mg were found to largely alter in natural aging, while that of Al-1.0&#37;Zn-4.2&#37;Mg little changed. After peak-aged heat treatments, the diamagnetism of Al-Zn-Mg was largely reduced. The binary Al-5&#37;Zn showed neither enhanced diamagnetism nor natural aging effect on the magnetization. Isothermal time variations of magnetization of Al-Zn-Mg alloys at 300 K were found to be related with solute-vacancy clustering. (C) 2018 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2018.10.037

Language：English   Publishing type：Research paper (scientific journal)  

Short crack growth behavior and its transitional interaction with 3D microstructure in Ti-6Al-4V

DOI： 10.1016/j.msea.2018.09.073

Repository Public URL： http://hdl.handle.net/2324/4123955

Language：English   Publishing type：Research paper (scientific journal)  

Microstructure evolution of alloy with composition Al - 3.4 Zn - 1.9 Mg (at. &#37;) was tracked using high resolution imaging and electron diffraction during ageing at 120 degrees C after being initially natural aged for 4 days. Hydrogen was charged in microstructure by cutting samples in Electrical Discharge Machine immediately after being quenched from solid solution temperature. Transmission Electron Microscope observations revealed a higher presence of high aspect ratio GPII-zones in microstructure of hydrogen charged and aged samples. Correlation was made with previously reported hydrogen effect into vacancy formation.

DOI： 10.1016/j.mtla.2018.09.035

Language：Japanese   Publishing type：Research paper (scientific journal)  

Size and distribution of micropores and voids in 5052 aluminum alloys during tensile deformation
<p>Micropore growth and void initiation and growth behaviors of 5052 aluminum alloys during tensile deformation were observed by means of X-ray computed tomography (CT) using the X-ray image beamline (BL20XU) of the Japanese synchrotron radiation facility (SPring-8). Tensile tests were carried out in ambient and wet conditions. In 5052 alloy tensile tested in wet condition, the drop of stress followed by the maximum stress was remarkable, and the fracture strain was reduced in comparison with those of 5052 alloy tested in ambient condition. The number of fine micropores and voids decreased in 5052 alloy when plastic deformation started and the decrease in the amount of fine micropores and voids in the wet condition was less than those in ambient condition. These might be caused by the acceleration of micropore growth and void initiation and growth during tensile testing in wet condition.</p>

DOI： 10.2464/jilm.68.630

Language：English   Publishing type：Research paper (scientific journal)  

First-principles calculation of multiple hydrogen segregation along aluminum grain boundaries

DOI： 10.1016/j.commatsci.2018.10.015

Language：English   Publishing type：Research paper (scientific journal)  

Synchrotron X-ray nanotomography, which offers a state-of-the-art resolution, has been applied for the 3D observations of hydrogen induced nano voids under different strain levels in Al-Zn-Mg-Cu aluminum alloys. A great number of nano voids are initiated uniformly across the whole specimen during a loading process. The average diameter and number density of initiated nano voids is 300nm and 5x10(15) m(-3), respectively. No evidence has been observed that the formation of nano voids results in the propagation of hydrogen induced quasi-cleavage cracks and premature fracture of Al-Zn-Mg-Cu aluminum alloys. Since nano void is one of the hydrogen trap sites in Al-Zn-Mg-Cu aluminum alloys, the majority of hydrogen can be repartitioned to nano voids during deformation due to their high density.

DOI： 10.2320/matertrans.m2018156

Repository Public URL： http://hdl.handle.net/2324/4485352

Language：English   Publishing type：Research paper (scientific journal)  

The Role of Hydrogen on the Local Fracture Toughness Properties of 7XXX Aluminum Alloys

DOI： 10.1007/s11661-018-4880-0

Language：Japanese   Publishing type：Research paper (scientific journal)  

Statistical evaluation of fracture of inclusions in cast aluminum alloy by massively-parallel voxel finite element analysis and geometrical measurements

DOI： 10.1299/transjsme.18-00028

Language：English   Publishing type：Research paper (scientific journal)  

First-principles study of hydrogen segregation at the MgZn2 precipitate in Al-Mg-Zn alloys

DOI： 10.1016/j.commatsci.2018.03.009

Language：English   Publishing type：Research paper (scientific journal)  

Atomic scale HAADF-STEM study of η′ and η1phases in peak-aged Al-Zn-Mg alloys
The microstructures of precipitates in Al-Zn-Mg alloys in peak-aged condition have been studied using scanning transmission electron microscope. The same thermo-mechanical treatment was applied in all alloys. Investigation of peak-aged samples revealed that the most commonly found phases were eta' and eta (1) with their respective habit planes on {111}(Al) and {100}(Al). eta' phases under [110](Al) were analyzed and compared with eta' structure models. Furthermore, a close inspection of eta (1) phase as the second most found precipitate revealed that it incorporates an anti-phase resembling boundary, not observed in other orientation relationships that precipitates create with Al matrix, in addition, differences in matrix-precipitate interfaces between eta'/eta (2) and eta (1) phases were noticed. This paper addresses the first part to the analysis of eta' phase. Next part is extended to the analysis of the eta (1) phase.

DOI： 10.1007/s10853-017-1873-0

Language：English   Publishing type：Research paper (scientific journal)  

Mapping 3D crystallographic orientation and strain fields in deformed polycrystalline aluminium alloy by diffraction-amalgamated grain boundary tracking

Language：English   Publishing type：Research paper (scientific journal)  

X-ray tomography is employed to observe the effects of intermetallic compound particles on the nucleation and growth of hydrogen micropores at high temperatures in Al-Zn-Mg-Cu aluminum alloys. Hydrogen micropores are heterogeneously nucleated on particles during exposure at 748 K. Growth and coalescence of the hydrogen micropores are observed with increasing exposure time. Interactions between hydrogen micropores and particles have a significant influence on the growth and coalescence of hydrogen micro pores. The growth speed of hydrogen micropores, nucleated on spherical, small particles is faster than those on other nucleation sites. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2017.03.020

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.actamat.2017.06.007

Language：Japanese   Publishing type：Research paper (scientific journal)  

Damage Behavior of Al-7&#37;Si Alloys with Refined Eutectic Silicon Particles due to Reduced Phosphor

DOI： 10.11279/jfes.89.239

Repository Public URL： http://hdl.handle.net/2324/4485344

Language：Japanese   Publishing type：Research paper (scientific journal)  

Precipitation structure and mechanical properties on peak-aged Al–Zn–Mg alloys including different with some Zn/Mg ratios

DOI： 10.2464/jilm.67.162

Language：Japanese   Publishing type：Research paper (scientific journal)  

Phase Contrast Imaging of Microsegregation of JIS ADCI2 Alloy and Damage Behavior

DOI： 10.11279/jfes.89.10

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： doi.org/10.2320/matertrans.M2016260

Language：English   Publishing type：Research paper (scientific journal)  

The combined effects of hydrogen micropores and intermetallic particles on the voids initiation and growth behavior of Al-Zn-Mg-Cu aluminum alloys during deformation and fracture are investigated with the help of the high-resolution X-ray tomography. It is interesting to note that the high-hydrogen concentration induced by an EDM cutting process results in the initiation of quasi-cleavage fracture near surface. With the increase of strain, the quasi-cleavage fracture is gradually replaced by dimple fracture. Voids initiation related to the dimple fracture is caused by both intermetallic particles fracture and interfacial debonding between particles and matrix. The nucleation of hydrogen micropores on intermetallic particles accelerates the voids initiation. The existence of triaxial stress ahead of the tip of a quasi-cleavage crack enhances growth rate for both hydrogen micropores and voids.

DOI： 10.1007/s11661-016-3773-3

Language：English   Publishing type：Research paper (scientific journal)  

The crack initiation mechanism of cast Al-Si-Mg alloy under low-cycle fatigue was addressed by using the synchrotron X-ray computed tomography (CT) and the image-based finite element analysis. The fatigue test and its in situ CT observation were conducted to visualize the crack initiation behavior. In the low-cycle fatigue, the cracking generally started with the voiding by the fracture of silicon particles, and the coalescence of these voids formed the crack. To elucidate the mechanism of silicon particle fracture, the finite element elastic-plastic analyses were performed with regard to twelve silicon particles including the fractured and intact particles detected by the chronological CT observation. By using the image-based modeling technique, the interested particle was embedded in the finite element model along with the surrounding particles as they were in the specimen. The material properties of silicon phase and aluminum matrix were identified by the nanoindentation tests. Ten cycles of loading by the uniform stress which was equivalent to the load in the fatigue test was applied to the finite element model, and the stress, strain and their cyclic response around the silicon particles were simulated. The morphology analysis was also carried out for the interested particles, and the geometrical parameters affecting the particle fracture were examined. By comparing the results of fractured and intact particles, we found that there were some geometrical conditions for the fracture of silicon particles, and a certain magnitude of hydrostatic stress was required to break the particles.

DOI： 10.1016/j.msea.2016.10.004

Language：English   Publishing type：Research paper (scientific journal)  

A comparison of the state of 3-D micro-damage induced by hydrogen redistribution due to thermal treatment and deformation near an intergranular fracture surface is carried out in high strength aluminium alloy using synchrotron microtomography. The mapping of various types of micro-damage provides evidence that hydrogen redistribution occurs along with a change in content and shape of micro-pores. The presence of intergranular cracks and an extended agglomerated micro-pore damage state are found to be in close proximity to each other, suggesting a mechanistic relationship for both formation of the unique damage architecture and insidious manifestation of embrittlement in high strength aluminium alloys. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.corsci.2016.04.050

Repository Public URL： http://hdl.handle.net/2324/4150460

Language：English   Publishing type：Research paper (scientific journal)  

Finite element analyses based on 3D images of the microstructure in an aluminum alloy observed by X-ray microtomography (so called image-based finite element analysis = IB-FEA) were performed to assess the influences of microstructures on ductile fracture behavior. The exact microstructural features of the aluminum alloy (i.e. hydrogen pores and particles) were perfectly reproduced in the FE models. The microstructural parameters (e.g. diameter, sphericity, volume of pores/particles) were quantified through a handmade software. IB-FEA provided indirect measure of ductility (or risk of ductile fracture), extracting the damage-/fracture-related values (e.g. z-axis normal stress, stress triaxiality and equivalent plastic strain) through simple elasto-plastic simulations. This made it possible to discuss the microstructure -ductility relationship. Dimensionality reduction of data was performed to filter out the microstructural parameters that do not contribute to ductility by quantitative analysis of the importance of the individual microstructural parameters. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2016.06.037

Language：English   Publishing type：Research paper (scientific journal)  

Hydrogen degrades the mechanical properties of high strength 7XXX aluminum alloys in two ways: (i) degrades the mechanical properties by hydrogen embrittlement, and (ii) partitioned into micropores as molecular hydrogen and make contributions to ordinary ductile fracture. The multifaceted effects of hydrogen on the mechanical properties of high Zn content 7XXX aluminum alloys during deformation and fracture is studied by using synchrotron X-ray microtomography. Our results have revealed that the hydrogen susceptibility has increased with increasing the Zn amount. High concentration of hydrogen was induced by the EDM wire eroder. This high concentrated hydrogen induces quasi-cleavage fracture and restricts the growth of micropores during ductile deformation. The threshold concentration of hydrogen ahead of the crack tip for the nucleation of quasi-cleavage feature was estimated to be .

DOI： 10.1007/s10704-016-0092-z

Language：English   Publishing type：Research paper (scientific journal)  

Quantitative tomography is carried out on datasets derived from tensile fracture sample of electrochemically precharged Al-Zn-Mg-Cu alloy in the underaged condition and its uncharged counterpart. It is shown that precharging which induces a transition of tensile fracture mode from ductile to brittle, results in a significant increase in micro-damage content in the regions near the fracture surfaces. Using quantitative tomography analysis based on spatial mapping of morphologically segmented micro-damage content of the datasets it is found that the precharged sample contains an inhomogenous distribution of micro-pores near grain boundaries. It is also shown that the spatial architecture of micro pores in the dataset is not influenced by the plastic zone of the intergranular cracks lying along the grain boundaries. Contrastingly the micro-pores in the tomographic dataset of the uncharged sample are shown to be present near intermetallic particles. It is therefore rationalized that the spatial architecture of micro-pores in the datasets from uncharged sample originate from particle cracking during ductile fracture, and from the tendency for damage enhancement by the synergism of hydrogen exposure near grain boundaries and localization of deformation in the precharged sample dataset. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2016.06.011

Repository Public URL： http://hdl.handle.net/2324/4149942

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.msea.2016.05.010

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

3D Fracture Behaviours in Dual-phase Stainless Steel

DOI： 10.2355/isijinternational.ISIJINT-2015-631

Language：English   Publishing type：Research paper (scientific journal)  

In theory, identification of material properties of microscopic materials, such as thin film or single crystal, could be carried out with physical experimentation followed by simulation and optimization to fit the simulation result to the experimental data. However, the optimization with a number of finite element simulations tends to be computationally expensive. This paper proposes an identification methodology based on nanoin-dentation that aims at achieving a small number of finite element simulations. The methodology is based on the construction of a surrogate model using artificial neural-networks. A sampling scheme is proposed to improve the quality of the surrogate model. In addition, the differential evolution algorithm is applied to identify the material parameters that match the surrogate model with the experimental data. The proposed methodology is demonstrated with the nanoindentation of an aluminum matrix in a die cast aluminum alloy. The result indicates that the methodology has good computational efficiency and accuracy. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijsolstr.2015.11.022

Language：English   Publishing type：Research paper (scientific journal)  

In the present study, combined thermal desorption spectroscopy (TDS), microtomography and X-ray diffraction study has been carried out to identify the hydrogen trap sites in 7XXX aluminum alloys. Through constant heating rate TDS experiments, three distinct trap states have been identified. It is revealed that micropores are the predominant hydrogen trap site in alloys with medium hydrogen content, whereas grain boundaries is the major hydrogen trap site in alloys with low and high hydrogen content. We have clarified that the rate of trap site occupancy in grain boundaries is high compared to dislocations and vacancies. Such high hydrogen coverage at grain boundaries indicates that the hydrogen-assisted fracture would be intergranular. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2015.12.092

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

A method to build an image-based model from a high-resolution X-ray CT image has been proposed for crystal plasticity finite element (CPFE) analysis in this study. The grain microstructures of aluminum alloy were captured by X-ray CT in synchrotron radiation facility, SPring-8. An image-based model of crystallographic grains was reproduced by the proposed method, and the model was analyzed by CPFE. By this, it was represented that deformation analysis of a polycrystal microstructure considering actual grain shapes was available suggesting that the deformation mechanism would be made clear by the image-based CPFE with further work.

DOI： 10.2320/matertrans.M2016260

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Biomineralization via microbiologically influenced corrosion induced by Pseudomonas aeruginosa biofilm

Language：English   Publishing type：Research paper (other academic)  

Non-destructive and three-dimensional measurement of local strain development during tensile deformation in an aluminium alloy
Anisotropy of mechanical responses depending on crystallographic orientation causes inhomogeneous deformation on the mesoscopic scale (grain size scale). Investigation of the local plastic strain development is important for discussing recrystallization mechanisms, because the sites with higher local plastic strain may act as potential nucleation sites for recrystallization. Recently, high-resolution X-ray tomography, which is non-destructive inspection method, has been utilized for observation of the materials structure. In synchrotron radiation X-ray tomography, more than 10,000 microstructural features, like precipitates, dispersions, compounds and hydrogen pores, can be observed in aluminium alloys. We have proposed employing these microstructural features as marker gauges to measure local strains, and then have developed a method to calculate the three-dimensional strain distribution by tracking the microstructural features. In this study, we report the development of local plastic strain as a function of the grain microstructure in an aluminium alloy by means of this three-dimensional strain measurement technique. Strongly heterogeneous strain development was observed during tensile loading to 30&#37;. In other words, some parts of the sample deform little whereas another deforms a lot. However, strain in the whole specimen was keeping harmony. Comparing the microstructure with the strain concentration that is obtained by this method has a potential to reveal potential nucleation sites of recrystallization.

DOI： 10.1088/1757-899x/89/1/012030

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2355/isijinternational.55.1483

Repository Public URL： http://hdl.handle.net/2324/4149938

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2355/isijinternational.55.1474

Repository Public URL： http://hdl.handle.net/2324/4149937

Language：English   Publishing type：Research paper (scientific journal)  

In recent years, a design concept for the stabilisation of the microstructure by addition of boron and nitrogen was developed. This so called martensitic boron-nitrogen strengthened steel (MARBN) combines boron strengthening by solid solution with precipitation strengthening by finely dispersed nitrides. Welded joints of MARBN steels showed no formation of a uniform fine grained region in the heat affected zone (HAZ) which is in general highly susceptible to Type IV cracking. In this work, the crossweld creep strength of a newly developed MARBN steel was analysed and the evolution of damage was investigated using synchrotron microtomography supported by electron microscopy. Three-dimensional (3D) reconstructions of the tested samples together with electron backscatter diffraction investigations revealed an intense void formation in a restricted area along small grains at prior austenite grain boundaries in the HAZ as the main reason for premature creep failures in the HAZ of welded joints.

DOI： 10.1179/1743284714Y.0000000621

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1179/0267083614Z.000000000853

Language：English   Publishing type：Research paper (scientific journal)  

The need for a new paradigm to estimate remaining creep life of service exposed steels is critically assessed. New approaches to residual life assessment are proposed, in the light of a decade's experience of the use of micro-tomography to characterise the three-dimensional (3D) nature of cavitation damage in structural materials. Imaging of conventional structural materials such as steels with high absorption to X-rays has been realised by synchrotron micro-tomography (SR-mu CT), providing new insights into phenomena such as creep failure. The unique feature of SR-mu CT studies is the direct imaging in 3D of cavities (hundreds of micrometres in size) present in the bulk, revealing the spatial characteristics and morphology of the creep voids. Quantitative analyses of the cavitation characteristics revealed by 3D datasets, when scaled with respect to time, stress and temperature, provide functional information suitable for developing constitutive equations for creep. The application of SR-mu CT, a non-destructive technique providing high fidelity data, significantly reduces the ambiguity in developing functional relationships to predict creep failure. The explicit use of such constitutive equations to estimate the residual life of components in creep, and the consequent assessment of structural integrity, would prove invaluable. Micro-tomography studies related to creep in materials are reviewed, with special emphasis on a 10.86&#37; Cr heat resistant steel, to demonstrate the type of data available for life assessment and design against creep failure. A brief discussion of current methods to estimate residual life in the light of recent 3D micro-tomography data follows. Finally, the possibility of new approaches, using micro-tomography data in conjunction with destructive 3D approaches such as serial sectioning, to formulate advanced residual life estimates, is briefly considered.

DOI： 10.1179/1743284714Y.0000000693

Repository Public URL： http://hdl.handle.net/2324/1813032

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1179/0267083614Z.000000000853

Repository Public URL： http://hdl.handle.net/2324/4149934

Language：English   Publishing type：Research paper (other academic)  

Growth behavior of hydrogen micro pores in Al-Zn-Mg-Cu alloys during high temperature exposure

Language：English   Publishing type：Research paper (scientific journal)  

Fatigue crack propagation behavior in a 7075-type Al alloy (Al-5.6%Zn-2.5%Mg-1.6%Cu) was investigated by applying Diffraction-Amalgamated Grain Boundary Tracking (DAGT), which provides grain morphologies and crystallographic orientations in three dimensions (3D). 3D crack morphologies at different propagation stages in the bulk of the sample were successfully obtained using synchrotron radiation X-ray microtomography (SRCT) technique. The apparent crack growth rate, da/dN, which varies significantly along a crack front line, was calculated. There are rapid acceleration and deceleration regions of da/dN due to the interaction with grain boundary (GB) and crack closure segments. Typical crack morphology under the influence of Mode II (in-plane shear) and Mode III (out-of-plane shear), such as crack deflection and twist, is detected by the observation of 2D tomographic slice image. A detailed direct assessment of microstructure-crack interaction behaviors has been achieved by applying the DAGT technique.

DOI： 10.2320/matertrans.M2014340

Language：English   Publishing type：Research paper (scientific journal)  

The formation behaviour of a blister in a die cast aluminium alloy was observed by employing a combined methodology of in situ three-dimensional observation using X-ray microtomography and image based simulation. It has been revealed, via a reverse approach based on the simulation, that nitrogen and carbon dioxide gases fill the blister nucleus. Spontaneous growth of the blister nucleus occurs through creep deformation of the surrounding aluminium due to the blister nucleus' high internal gas pressure. This internal gas pressure also induces hydrogen precipitation in the form of micropores, which undergo steady growth in a spherical shell region around the blister nucleus. The selective growth of the micropores is attributable to the elevation of hydrostatic stress in directions parallel to the casting surface, thereby promoting the expansion of the blister, also parallel to the casting surface, through the absorption of surrounding micropores into the blister nucleus.

DOI： 10.1179/1743133614Y.0000000123

Language：English   Publishing type：Research paper (scientific journal)  

The formation behaviour of a blister in a die cast aluminium alloy was observed by employing a combined methodology of in situ three-dimensional observation using X-ray microtomography and image based simulation. It has been revealed, via a reverse approach based on the simulation, that nitrogen and carbon dioxide gases fill the blister nucleus. Spontaneous growth of the blister nucleus occurs through creep deformation of the surrounding aluminium due to the blister nucleus’ high internal gas pressure. This internal gas pressure also induces hydrogen precipitation in the form of micropores, which undergo steady growth in a spherical shell region around the blister nucleus. The selective growth of the micropores is attributable to the elevation of hydrostatic stress in directions parallel to the casting surface, thereby promoting the expansion of the blister, also parallel to the casting surface, through the absorption of surrounding micropores into the blister nucleus.

DOI： 10.1179/1743133614Y.0000000123

Language：Japanese   Publishing type：Research paper (scientific journal)  

Effect of Phosphorus Content on Mechanical Properties in Al-7&#37;Si Alloy

DOI： 10.11279/jfes.86.832

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Other Link： http://www.spring8.or.jp/pdf/en/res_fro/13/112_113.pdf

Language：English   Publishing type：Research paper (other academic)  

Application of Diffraction‐Amalgamated Grain Boundary Tracking (DAGT) to Fatigue Crack Propagation Behavior in High Strength Aluminum Alloy

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/s1003-6326(14)63317-3

Language：English   Publishing type：Research paper (other academic)  

A novel experimental method has been developed by amalgamating a pencil beam X-Ray diffraction (XRD) technique with the recently developed grain boundary tracking (GBT) technique. XRD and GBT are both non-destructive in-situ analysis techniques for characterizing bulk materials, which can be carried close to the point of fracture. DAGT provides information about individual grain orientations and 1-micron-level grain morphologies in 3-dimensions (3D) together with high-density local strain mapping. An Al-3 mass &#37; Cu model alloy was used to investigate its deformation behavior under tension. The morphology of the grains was determined by the X-ray microtomography (XMT) imaging and the liquid metal wetting technique, after which GBT provided an accurate description of the position and morphology of all the grains in a region of interests. Diffraction spots in the XRD experiments were related to grains, making it possible to describe crystallographic orientation of all the grains. It has been revealed that deformation is localized at both microscopic and meso-scopic levels. Inhomogeneous deformation was observed in each individual grain. In addition, a group of a few grains coordinately interacts and specific grain boundaries thereby exhibit intense strain localization. Hydrostatic tension was also observed at quadruple junction points and its mechanism was analyzed.

DOI： 10.4028/www.scientific.net/MSF.794-796.57

Language：English   Publishing type：Research paper (scientific journal)  

A Numerical Evaluation of an Infill Sampling Criterion in Artificial Neural Network-Based Optimization

DOI： 10.7763/ijcte.2014.v6.874

Repository Public URL： https://hdl.handle.net/2324/7157420

Language：English   Publishing type：Research paper (scientific journal)  

A Method for the Identification of Mechanical Properties Using Surrogate Models

DOI： 10.7763/ijcte.2014.v6.868

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4028/www.scientific.net/MSF.794-796.325

Language：English   Publishing type：Research paper (scientific journal)  

Fundamental Assessments of Application of Fluidized Bed Furnaces to Solution and Aging Treatments in Al-Mg-Si Castings

DOI： 10.11279/jfes.86.209

Language：English   Publishing type：Research paper (scientific journal)  

It has generally been assumed that metals usually fail as a result of microvoid nucleation induced by particle fracture. Here, we concentrate on high-density micropores filled with hydrogen in aluminum, existence of which has been largely overlooked until quite recently. These micropores exhibit premature growth under external loading, thereby inducing ductile fracture, whereas the particle fracture mechanism operates only incidentally. Conclusive evidence of a micropore mechanism is provided by the observation of an instantaneous release of gas at failure. We can therefore conclude that the growth of micropores dominates ductile fracture. Since the material we used has a standard pore density, we can assume that an identical fracture mechanism operates in other aluminum alloys. This finding suggests that intense heat treatment, which is generally believed to enhance the mechanical properties through homogenization, may have entirely the opposite effect. This revelation will have a major impact on the engineering design of metals. (C) The Minerals, Metals & Materials Society and ASM International 2013

DOI： 10.1007/s11661-013-2013-3

Language：English   Publishing type：Research paper (scientific journal)  

It has generally been assumed that metals usually fail as a result of microvoid nucleation induced by particle fracture. Here, we concentrate on high-density micropores filled with hydrogen in aluminum, existence of which has been largely overlooked until quite recently. These micropores exhibit premature growth under external loading, thereby inducing ductile fracture, whereas the particle fracture mechanism operates only incidentally. Conclusive evidence of a micropore mechanism is provided by the observation of an instantaneous release of gas at failure. We can therefore conclude that the growth of micropores dominates ductile fracture. Since the material we used has a standard pore density, we can assume that an identical fracture mechanism operates in other aluminum alloys. This finding suggests that intense heat treatment, which is generally believed to enhance the mechanical properties through homogenization, may have entirely the opposite effect. This revelation will have a major impact on the engineering design of metals.

DOI： 10.1007/s11661-013-2013-3

Language：English   Publishing type：Research paper (scientific journal)  

It has recently been reported that aluminum alloy ductile fracture is dominated by micropore growth, whereas the particle fracture mechanism operates incidentally. The effects of stress triaxiality in front of a notch or crack were here investigated by employing microtomography observations. A fractional dimple pattern area originating in micropores increased with the increase in stress triaxiality on fracture surfaces. This implies that the effects of micropores on mechanical properties are more pronounced in notched and cracked materials.

DOI： 10.2320/matertrans.L-M2013841

Language：English   Publishing type：Research paper (scientific journal)  

Three-dimensional W-concentration mapping is attempted in a high speed tool steel, SKH51 by applying K-absorption edge subtraction imaging utilizing high energy X-ray in synchrotron radiation facility. Effect of a sample-to-detector distance on spatial resolution had already been reported in high-energy X-ray microtomography. Therefore, effect of the sample-to-detector distance on W-concentration obtained by the Kabsorption edge subtraction imaging has been assessed in this study. A fine CT image was obtained in 65 mm sample-to-detector distance with the influence of both scattering and diffraction on spatial resolution. Although image quality depended on sample-to-detector distance, the distance did not affect Wconcentration measured by the absorption edge subtraction imaging so much, because the effect is limited on object interface. The average W-concentration in whole specimen was consistent with the chemical composition in the SKH51 steel. The maximum W-concentration also agreed with the SEM-EDS result. It was not easy to assess W-concentration on a carbide particle by means of segmentation based on a linear absorption coefficient. The average W-concentration at an aggregated particle, which looks a large coarse particle in CT image, corresponded to the average W-concentration that was estimated based on SEM-EDS. Therefore, it was concluded that W-concentration obtained by K-absorption edge subtraction imaging was accurate. Three-dimensional W-concentration mapping was available in steels by dual-energy K-absorption edge subtraction imaging utilizing high energy X-ray.

DOI： 10.2355/isijinternational.54.141

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Fundamental Assessments of Application of Fluidized Bed Furnaces to Solution and Aging Treatments in Al-Mg-Si Castings

Language：Japanese   Publishing type：Research paper (scientific journal)  

Effect of Phosphorus Content on Mechanical Properties in Al-7%Si Alloy

Language：English  

The crack initiation mechanism of cast aluminum alloy was addressed to quantitatively evaluate the fatigue strength. We employed the synchrotron radiation microtomography to visualize the three-dimensional damages around pores and silicon particles. Two types of specimens underwent a low-cycle fatigue test. The temperature of solution treatment was different, and it yielded a difference in the shape, size and distribution of silicon particles. After a certain cycles of fatigue, a catastrophic damage around many silicon particles occurred, and they connected to each other so as to form a crack especially within the high stressed region around a relatively large pore. The scanning electron microscopy after the test showed that the type of damage was the breakage of long-shaped silicon particles or the aluminum-silicon interface debonding of round silicon particles. The high temperature solution treatment facilitated the interface debonding by the enlargement of silicon particles.

DOI： 10.2464/jilm.64.570

Language：English  

The presence of heterogeneous deformation is a one of key issue in a prediction model of deformation texture development. Recently, not only local strain mapping but also crystallographic orientation mapping is possible to obtain within aluminum alloy by using synchrotron radiation. In this study, local strain mapping and orientation mapping were obtained by microtomography and three-dimensional X-ray diffraction using synchrotron radiation in Al - 4Pb alloy. Simulation of deformation texture evolution has been performed based on crystal plasticity model. The simulation started from actual microstructure and the obtained local strain was applied. The simulation produced similar microstructure to the actual one. Therefore, heterogeneous strain distribution is very important for the development of deformation texture.

DOI： 10.2464/jilm.64.557

Language：English  

DOI： 10.2464/jilm.64.518

Language：English  

DOI： 10.2464/jilm.64.510

Language：English  

DOI： 10.2464/jilm.64.611

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.2464/jilm.63.452

Language：English  

In the present study, various microstructural features, such as particles and pores, have been visualized in cast and wrought aluminum alloys by employing X-ray tomography apparatuses with a wide range of spatial resolution. Special care is dedicated to evaluate an identical sample for each entire series of imaging experiments. The X-ray tomography apparatuses used include the one performed at a synchrotron radiation facility, which has a spatial resolution level close to the theoretical limit of the projection-type imaging, in addition to two industrial apparatuses. It has been shown that even if industrial apparatuses, which inevitably possess limited spatial resolution levels, are used, the real size and fraction of microstructural features can be estimated by performing imaging experiments above a certain spatial resolution level. It would be, so far as the authors are aware, the first time to demonstrate the feasibility of laboratory-scale X-ray tomography imaging in microstructural observation in a systematic manner, especially focusing on spatial resolution and quantitative capability.

DOI： 10.2464/jilm.63.343

Language：English  

In this study, evaluation of precision in rotation stage and investigation of effect of rotation stage blurring on resolution are performed in imaging X-ray tomography set-up, which allows nano-scale observation, for the purpose of improving resolution in X-ray tomography. In the result of precision evaluation of rotation stage in high-resolution imaging X-ray tomography, fluctuation, which was approximately 35 nm in maximum and approximately 13 nm in average, was found. This fluctuation was under 1 pixel. In the simulation that analyzed effect of fluctuation in rotation stage, it was found that long periodic fluctuation deteriorate reconstructed image terribly. But, impulse-like fluctuation does not almost affect reconstructed image quality. However, reconstructed image is deteriorated when the frequency of impulse-like fluctuation increase. If long periodic fluctuation, which was observed in the precision evaluation, is corrected, the resolution improvement was confirmed though the fluctuation was less than 1 pixel.

DOI： 10.2464/jilm.63.273

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

The paper provides an insight into the development of the micro-pore damage phenomenon during the hydrogen ingress and egress in a high strength aluminum alloy. High resolution micro tomography scans on samples subjected to combinations of cathodic hydrogen charging and de-sorption heat treatment were carried out. The quantitative analysis, spatial mapping, and probabilistic evaluation of the 3D datasets revealed that the development of micro-pore damage during hydrogen ingress-egress had a non-trivial dependence on the particle size distribution. This provides a rationale to mitigate the deleterious effects of hydrogen in aluminum alloys by controlling particle size characteristics. (C) 2013 AIP Publishing LLC.

DOI： 10.1063/1.4826274

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English  

The aim of this study was to establish a novel orientation analysis method that utilizes accurate grain position information, obtained by grain boundary tracking, to enable crystal-plasticity deformation analysis of polycrystalline metals. An experiment combining X-ray tomography and X-ray diffraction was performed, and the feasibility of the method was assessed by confirming the relation between diffraction spots and grains whose position was obtained by grain boundary tracking. Although some deviations were observed in diffraction spot intensity, owing to lack of beam stability and the extinction effect, several combinations of grain and spot features showed a high correlation. Furthermore, the diffraction spots originating from grains whose position was detected using grain boundary tracking showed higher correlation coefficients than those originating from grains whose position was detected using 3DXRD. In the case of the former grains, we could easily identify diffraction spots originating from specific grains by focusing on sets of grain and spot features having a high correlation. It was demonstrated that setting appropriate tolerance level enabled highly accurate orientation analysis, almost equivalent to that of 3DXRD.

DOI： 10.2320/jinstmet.J2013006

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

A procedure for determining three-dimensional grain boundary geometry and its change under external loading is proposed for evaluating crystallographic deformation behaviours in polycrystalline materials, and the feasibility of this approach is confirmed for an aluminium alloy. X-ray microtomography has been combined with gallium-enhanced microscopy, in which grains are visualized in three dimensions by decorating grain boundaries with liquid gallium. Grain boundary particles are then extracted by comparing tomographic images with and without the gallium application. Three-dimensional reconstruction of grains is achieved using a connection scheme based on triplets of non-aligned points on grain boundaries. The deformation of the closed polygonal grains is visualized by combining the above technique with a microstructural tracking technique, in which the paths of particles are reconstructed by matching each pair of particles in consecutive images. This process also enables high-density four-dimensional strain mapping by tracking particles located in grains, providing direct interpretation of localized deformation caused by interaction between neighbouring grains. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2013.06.013

Language：English   Publishing type：Research paper (scientific journal)  

Utilization of synchrotron X-ray microtomography has enabled the virtual reconstruction of invisible microstructural units and their deformation during the compaction, compression and recovery of flexible graphite. Particles artificially affixed, in advance, to the surface of a given microstructural unit were connected by plane triangles to create a 3D mesh in the reconstruction. High density 3D mapping of strain and displacement has also been achieved, by tracing the physical displacement of the surface particles. Micro-mechanisms of compression and recovery behavior in flexible graphite have been examined involving the direct observations and measurements. The microstructural unit was found to be composed of thin expanded graphite discs with slightly misaligned basal planes of graphite. Highly localized deformation of a thin expanded graphite disc was observed during the compression and recovery processes, suggesting strong interaction with surrounding expanded graphite discs. The macroscopic compression behavior of flexible graphite is attributable to a combination of bending and thickness reduction/recovery of the discs. It has, however, been shown that only the thickness recovery of the individual discs, due to the presence of internal entrapped air, accounts for the macroscopic recovery behavior of flexible graphite. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2013.03.008

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

The localizations of plastic deformation in shear band which initiated at the ahead of crack tip of 7075 aluminum alloys have been investigated via in-situ fracture tests using synchrotron X-ray tomography. Local crack driving forces and local strain distributions were measured from tomographic images. The distributions of crack-tip opening displacement along a crack front line were found to vary randomly across specimen thickness. This was attributed to the interaction of stress shielding/anti-shielding effects. The strain distributions around crack-tip were quite different from the understanding which was derived by the elastic-plastic fracture mechanics. With further loadings, the development of equivalent strains in shear bands increased leading to the localizations of plastic deformation. The widths of shear band were observed to decrease at the same time. The degree of localization was affected not only by well-known factors such as aging conditions but also polycrystalline texture and crystallographic orientation. Beyond more than ten times as large strain region which is defined by the fracture mechanics, particles were damaged with developing shear band. Thus, extensive damage within shear bands has been induced the complex behavior of crack propagation in practical materials.

DOI： 10.2464/jilm.63.188

Language：English   Publishing type：Research paper (scientific journal)  

The influences of work hardening behavior of materials on ductile fracture, and especially on void growth and coalescence, have been investigated in model materials by in-situ X-ray computed tomography (XCT) coupled with tensile deformation. The model materials contain an artificial void array embedded in a metal matrix. By producing such materials with different metal matrices (pure copper, brass, Glidcop = copper strengthened by Al₂O₃ nanoparticles), the influences of the work hardening behaviors on void growth and coalescence/linkage process are analyzed. This set of experiments were performed at Japanese synchrotron radiation facility SPring-8 BL20XU beamline, whereby the X-ray tomography setup with one of the highest spatial resolution in the world is available. This beamline however provides less brilliant X-rays compared to the ESRF ID15 beamline where the our previous experiments were performed Hosokava et al. (Acta Mater, 60:2829-2839, 2012), (Acta Mater, 61:1021-1036, 2013). To compensate for the X-ray absorption problems, the specimens to be tested have to be much smaller, making the experiments more difficult. Nevertheless, the growth and linkage behaviors of the artificial voids were successfully visualized, and the plastic strain whereby the linkage takes place (referred to as the linkage strain, hereafter) were quantitatively captured. The models for void coalescence developed by Thomason and by Pardoen and Hutchinson both predict coalescence rather well for both brass and Glidcop, even though the linkage events were found to be dominated by the meso/macro shear localization process.

DOI： 10.1007/s10704-013-9820-9

Language：English   Publishing type：Research paper (scientific journal)  

It has recently been revealed that high-density pre-existing hydrogen micropores, formed during production processes, exhibit premature growth and coalescence under external loading at room temperature, thereby inducing ductile fracture. This process is incidentally supplemented by the well-established ductile fracture mechanism based on particle damage. It is reasonable to assume that the pre-existing hydrogen micropores may also contribute to damage evolution at high temperatures. In the present study, synchrotron X-ray microtomography was applied to the in situ observation of deformation and fracture in Al-Mg alloys at a high temperature. High-density hydrogen micropores were observed in the alloys. Flow localization controlled deformation through the mechanism of solute drag creep. A combined effect of grain boundary sliding and heterogeneous nucleation on particles was also confirmed to accelerate the growth of pre-existing hydrogen micropores and cavities. Although continuous nucleation occurred together with the growth of pre-existing hydrogen micropores, the effects of the pre-existing hydrogen micropores, especially those located on grain boundaries, were predominant in the overall damage evolution. It seemed likely that supersaturated hydrogen in the aluminum alloys might also make an appreciable contribution to cavitation during high-temperature loading. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2013.01.012

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.11279/jfes.85.205

Language：English   Publishing type：Research paper (scientific journal)  

The internal microstructure of the high strength AlZnMg foam was characterized via the synchrotron-based X-ray microtomography. Using three-dimensional (3D) quantitative image analysis of the tomographic dataset, the microstructural features, such as content, size distribution, shape, and spatial distribution of micropores inside the cell wall, were determined. Together with a dual energy imaging technique, the 3D distribution of Zn in the alloyed foam was assessed by the subtraction of two images acquired above and below the Zn K-absorption edge. The damage behavior of the alloyed foam was also clarified by this element sensitive imaging technique.

DOI： 10.1002/adem.201200142

Language：English   Publishing type：Research paper (scientific journal)  

Two three-dimensional (3-D) techniques, namely X-ray microtomography and serial sectioning, have been applied for characterization of creep cavitation behavior in tempered martensitic steel. For this purpose samples have been extracted from a series of specimens that were subjected to creep tests over the stress range of 120-180 MPa at 600 degrees C. The presence of creep voids in the series of samples was unambiguously detected in a non-destructive manner using synchrotron X-ray microtomography with a resolution of 1 gm. The 3-D visualization of the datasets provided an assessment of the spatial distribution and morphology of the creep voids as a function of creep stress and high temperature exposure time. The quantitative analyses of the image datasets enabled the development of functional relationships between the macroscopic creep parameters (such as rupture ductility, applied stress, creep life) and cavitation characteristics (such as volume fraction, and number density). The quantitative analyses also provided an evaluation of manifestations of growth and coalescence processes in the respective datasets. A transition of cavitation behavior of the steel has been found to occur in the stress range of 120-150 MPa at 600 degrees C. The evolution in the pattern of cavitation and its relation to the prior-austenite boundary was explored by combining micro-tomography and serial sectioning techniques, which revealed a new possibility in the progress of cavitation in the long term creep exposed specimens of 9-12&#37; Cr heat resistant steels. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2012.12.002

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

It has been reported that most aluminum alloys contain high-density micro pores which make an appreciable contribution to damage evolution during ductile fracture. It is reasonable to assume that the mechanical properties of aluminum alloys are more or less improved by controlling micro pores in aluminum alloys. In the present study the volume fraction of micro pores is controlled by controlling hydrogen content over a wide range. Tensile tests are performed using smooth and notched specimens at room and elevated temperatures together with a fracture toughness test. It has been shown that both strength and ductility increase with decreasing micro pore volume fraction. The elimination of micro pores has pronounced effects especially on high-temperature ductility notched tensile strength and fracture toughness. It has been observed in the in-situ observation of a room temperature tensile test that pre-existing hydrogen micro pores exhibit premature growth immediately after the onset of plastic deformation whereas the well-known particle fracture mechanism operates only after the maximum load in the alloys with the least micro pores fraction. It can be inferred that in the notched and pre-cracked specimens the premature growth of micro pores are driven by triaxial stress state thereby inducing more degradation in mechanical properties.

DOI： 10.2320/matertrans.L-M2013832

Language：English   Publishing type：Research paper (scientific journal)  

Spatial resolution of three-dimensional images obtained by synchrotron X-ray microtomography technique is evaluated using cyclic bar patterns machined on a steel wire. Influences of X-ray energy and the sample-to-detector distance on spatial resolution were investigated. High X-ray energies of 33-78 keV are applied due to the high X-ray absorption of transition metals. Best spatial resolution of about 1.2 μm pitch was observed at the sample-to-detector distance range of 20-110 mm and at the energy range of 68-78 keV. Several factors such as X-ray scattering and diffraction phenomena affecting the degradation of spatial resolution are also discussed. © 2012 American Institute of Physics.

DOI： 10.1063/1.4773239

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (other academic)  

Time-resolved 3D measurements of mechanical behaviours in aluminium alloys

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (other academic)  

Development of diffraction-amalgamated grain-boundary tracking technique and its application to polycrystalline metals
By amalgamating a transmission X-Ray diffraction (XRD) experiment with grain boundary tracking (GBT) that has been developed by the present authors by combining the X-ray micro-tomography (CT) and the gallium-enhanced grain boundary visualization techniques, a novel method which provides accurate crystallographic information of individual grains during deformation has been created. The developed technique, which is called diffraction-amalgamated grain boundary tracking (DAGT) technique, is non-destructive for in-situ characterizing of bulk materials, which allows for close to deformation and fracture analysis of metals. Employing near field XRD analysis with a thin collimated X-ray beam, the algorithms developed for DAGT identifies which diffraction spots are related to which grain; consequently, providing a description of the misorientation between grains. DAGT also realizes micron-level analysis of grain morphologies and local stain distribution in 3-dimensions (3D) on the basis of CT observation, enabling the crystallographic interpretation of localized deformation without being affected by blurring of diffraction spots caused by deformation. An Al-3mass&#37; Cu alloy was used for demonstration purpose.

DOI： 10.1117/12.930608

Language：English   Publishing type：Research paper (scientific journal)  

The compression and unloading behavior of flexible graphite sheets was investigated using synchrotron radiation microtomography with 1 gm voxel size. The recovery ratio of the flexible graphite sheet was measured accurately by in-situ observation. The three-dimensional strain distribution in the interior of the specimen was obtained using the microstructural tracking method. The inner strain distribution with micrometer scale indicated inhomogeneous deformation. The microstructural tracking analysis revealed that deformation units exist in the flexible graphite sheet. The units seem to deform, affecting the neighboring units with each other. The units had a similar size and shape with compacted exfoliated graphite worms that constitute the flexible graphite sheet. Microscopic deformations during compression and unloading are surely affected by the microstructure of the sheet. Crown Copyright (C) 2012 Published by Elsevier Inc. All rights reserved.

DOI： 10.1016/j.matchar.2012.04.008

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2355/isijinternational.52.516

Language：English   Publishing type：Research paper (scientific journal)  

Cast aluminium alloy has sometimes been utilised for various products after applying plasticworking combining with heat treatment. The thermomechanical treatment will bring not onlypositive effects (workhardening and grain refinement) but also negative effects (damage onparticles and increase of porosity) on the mechanical properties in the cast aluminium alloy. In thisstudy, the relation between microstructures and fatigue properties has been investigated in hotforged and heat treated Al-Si-Mg casting alloys with different Si contents. An ex situ observationof fatigue crack propagation showed different crack behaviours depending on the microstructuresarising from the different Si contents. The crack in the &amp
alpha
phase propagated quickly incomparison with the crack located in the eutectic and grain boundaries in the Al-3&amp
middot
1Si-0&amp
middot
4Mgalloy. The crack propagation rate was not constant in the Al-7&amp
middot
7Si-0&amp
middot
4Mg alloy due to theagglomerated Si particles in the eutectic region. © 2012 W. S. Maney &amp
Son Ltd.

DOI： 10.1179/1743133611Y.0000000012

Language：Others   Publishing type：Research paper (scientific journal)  

On the basis of sudden change of linear absorption coefficient (LACs) in the vicinity of absorption edge, the synchrotron K-edge subtraction technique is developed to label the three-dimensional (3D) distribution of element. In this work, tomographic scans above and below the specific absorption edge of Zn are carried out and the subtracted image is used to identify and quantify the 3D distribution of Zn element inside the cell wall of Al-Zn-Mg foam. A non-uniform spatial distribution of Zn element is found in the cell wall of as-cast foam. After long solution tratment, the concentration of Zn element tended to be homogeneous. It is confirmed that the local agglomerated Zn-bearing particles exerta negative influence on the brittle cracking of the cell wall. The K-edge subtraction technique provides a powerful tool for the quantitative microstructure characterization of three-dimensional tissues.

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2464/jilm.61.402

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4028/www.scientific.net/.249

Language：English   Publishing type：Research paper (scientific journal)  

In material engineering, it is widely recognized that deformation and fracture (D/F) characteristics are important because the safety of developed materials can be determined on the basis of D/F characteristics. The D/F characteristic is defined as the load required to break the material and the strain caused by applying a particular load. To observe the effect of grain boundary slip at the micron level, we have proposed a method of obtaining displacement vectors of internal structures from submicron 3D CT images. In this paper, we introduce an improved method for accurately acquiring D/F characteristics. The results of a simulation and a real test confirm the effectiveness of the improved method.

DOI： 10.1541/ieejias.131.548

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.2464/jilm.61.402

Language：English   Publishing type：Research paper (scientific journal)  

It has recently been discovered that micropores on the order of a few microns agglomerate in a high density in the sub-surface layer of aluminum alloys that have been produced in a high-quality die-casting process. It is known that fatigue behavior is dominated by the existence of the micropores. In the present study, geometrical parameters defining the relationship between fatigue crack initiation and micropores have been investigated using high-resolution X-ray microtomography, combined with two kinds of statistical analysis. It has been revealed that consideration of micropore pairs is necessary, and a number of parameters for paired micropores that may be strongly associated with fatigue crack initiation have been extracted and statistically evaluated. It is concluded that the mean diameter between paired micropores, and the mean distance to the casting surface, are predominant in fatigue crack initiation. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2011.04.049

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.proeng.2011.04.427

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Fast microtomography combined with local crack driving force analysis has been employed to analyze crack-tip stress/strain singularities in an aluminum alloy. The application of fast microtomography has made it possible to observe real crack initiation and propagation behaviors without intermediate unloading. The details of a crack and its local propagation behaviors are readily observed with this technique along with evidence of microstructure/crack interactions. After a preliminary investigation of the achieved spatial resolution, we show that conventional stationary and growing crack singularities can be quantitatively validated by deriving the local crack opening displacement. This is to our knowledge the first three-dimensional validation of conventional fracture mechanics during a real time continuous experiment that has been mainly developed via surface observations so far. We also reveal that there is a spatial transition from a stationary crack singularity to a growing crack singularity in addition to the well-known temporal transition that occurs with the onset of crack propagation. Local crack propagation behaviors are also discussed on the basis of this validation. To separate the effects of complex crack geometry from those of microstructure, we also perform an image-based numerical simulation. (c) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2010.11.065

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Dual-energy K-edge subtraction imaging technique has been employed to analyze the spatial distribution of copper and its change in three-dimensions quantitatively during a solution treatment. In order to realize it, some preliminary investigations on the verification and assurance of accuracy and repeatability have been performed. Inhomogeneous Cu concentration distribution is revealed even after the solution treatment for a sufficiently long period of time at a high temperature in an Al-Cu alloy. The present technique has a unique potential to realize four-dimensional chemical-concentration mapping. [doi:10.2320/matertrans.L-M2010819]

DOI： 10.2320/matertrans.L-M2010819

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2464/jilm.60.409

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

In the past, deformation/fracture (D/F) characteristics, defined as load-deformation relationships until the materials are fractured, have been analyzed and evaluated on the surface. The D/F characteristics are affected by more than 10,000 micro-scale internal structures like air bubbles (pores), dispersed particles and cracks in 1 mm(3); therefore, it is required to analyze nano-scale D/F characteristics inside materials. In this paper, we propose an analysis method by obtaining displacement vectors of dispersed particles from nano-order 3D-CT images. A problem of matching over 10,000 dispersed particles between deformation is solved by a stratified matching.

DOI： 10.1007/s00138-009-0242-7

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4028/www.scientific.net/MSF.638-642.378

Language：English   Publishing type：Research paper (scientific journal)  

Porosity in Al-Si-Mg cast alloys utilised in automotive parts affects directly products quality, i.e. mechanical properties. In this study, the effect of micropores on mechanical properties has been investigated by X-ray tomography from the viewpoint of clustering micropores. The local volume fraction (LVF) of porosity was introduced to analyse the effect of clustering micropores. The statistical Weibull method was also used in order to explain strength of the alloy tested. The fracture strain decreased drastically from 17 to 3&#37; on an inverse parabolic relationship with increasing porosity. In the case of the specimens that contain the largest pore higher than 100 mm, the ultimate tensile strength decreases monotonically. It is found that the fracture surface passes through high LVF regions. The fracture strain obviously depends on the ratio of LVF higher than 10&#37;. It is confirmed that the LVF, which represents unevenly distribution of micropores cluster, is one of important dominant factor for managing the mechanical properties in the Al-Si-Mg cast alloy.

DOI： 10.1179/174328409X441283

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4028/www.scientific.net/MSF.638-642.2523

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4028/www.scientific.net/MSF.654-656.2303

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.4028/www.scientific.net/AMR.89-91.449

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

The annihilation behavior of micro pores in an aluminum alloy casting during surface cold working was continuously observed using the synchrotron radiation microtomography. To analyze micro pore annihilation behavior, the displacement of artificially dispersed particles was measured and thereby local strain distributions were mapped in high-density. A peening treatment annihilated most of the micro pores with a diameter of over 10 mu m in the upper part of the specimen that could initiate fatigue cracks. The annihilation behavior of the micro pores could be understood as a function of effective strain locally accumulated around them, and not as a function of local hydrostatic strain. The effective strain varied significantly, with some large pores remaining where local effective plastic strain was relatively low. The complete annihilation of large pores in the surface layer suggests that the application of sufficiently long surface cold working is effective in improving the high-cycle fatigue properties. [doi: 10.2320/matertrans.M2010069]

DOI： 10.2320/matertrans.M2010069

Language：English   Publishing type：Research paper (scientific journal)  

There have been no significant investigations into the effects ofinsulators on auditory impressions. Consequently, in our previous study wecarried, out research on economical and, ecological insulators with layers ofaluminum, waste material and, gray cast iron and established the effects oflayered construction on auditory impressions. In this study, we carried, outfurther research on other economical and, accessible materials that have bettercharacteristics than those previously investigated, and determined theirmaterial characteristics for auditory impressions. We determined the dampingcharacteristics of the insulators using the integrals of their power spectrumsin the vicinity of the power spectrum, peaks. Furthermore, we established, thatthe envelope curve for the impulse response of the insulators had differentmaterial characteristics and conveyed different auditory impressions. ICIC International

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2464/jilm.60.190

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/14786430903571438

Language：English   Publishing type：Research paper (scientific journal)  

It has been demonstrated that the strength of an Al-Si-Cu alloy is maximized by high-temperature solution treatment at 807 K, which is approximately 16 K higher than the ternary eutectic temperature. The dual-energy K-edge subtraction imaging technique has been employed to obtain the spatial distribution of copper and its change during its solution treatment in three dimensions quantitatively, providing interpretations of the improved mechanical properties in terms of age-hardenability and its spatial variation. It has been also confirmed that the occurrence of incipient local melting and the accompanying growth of micro pores adjacent to the melt regions lead to fractures caused by these defects. However, it can be inferred that the positive effects can outweigh the negative effects even above the eutectic temperature, thereby realizing the maximum strength at such relative high temperature levels. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2009.11.044

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Inspired by a success in applying a fluidized bed furnace to high-temperature solution treatments, the present authors have attempted to modify the age-hardening characteristics of Al-Mg-Si alloys by utilizing its superior heating rate. Two-step ageing treatments have been applied to five kinds of alloys with different Mg ₂Si and excess Si contents. Heating rates for the first and the second ageing treatments have been varied as well as ageing temperature for the first ageing treatment. It has been clarified that the rapid heating to the first ageing temperature enhances strength compared to the standard T6-temper for all the alloys tested, especially for a balanced alloy with a low Mg ₂Si content. It has been confirmed that small precipitates are formed in high density in such cases. In most cases, the improvements in hardness have been observed by adding the ageing treatment at 353 or 373 K for only 0.8 ks before the ordinary ageing at 450 K. We attribute this to the suppression of unfavorable clusters which ordinarily form below those temperatures during heating.

DOI： 10.2464/jilm.59.569

Language：English   Publishing type：Research paper (scientific journal)  

Synchrotron X-ray microtomography was used to observe the shrinkage and annihilation behaviors of hydrogen micropores in three dimensions during hot and cold plastic deformation of an Al-Mg alloy. Whether complete healing of micropores is achieved after plastic deformation was examined by exposing the material to a high temperature after plastic deformation. Although micropores generally show a pattern of shrinking and closing, closer inspection of a single specimen revealed a variety of geometrically variable behaviors. It is noteworthy that some of the micropores are reinitiated in positions identical to those before their annihilation, even after an 8-22&#37; macroscopic strain has been further applied after annihilation. We attribute local variations such as these to significant local strain variation, which we measured in a series of tomographic volumes by tracking the microstructural features. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2009.06.012

Language：English   Publishing type：Research paper (scientific journal)  

To study fatigue cracking behavior, an improved microstructural tracking method is used to calculate the local crack driving forces in a fatigue crack in an aluminum alloy by employing high-resolution in situ synchrotron X-ray micro tomography. Several valuable insights into actual three-dimensional fatigue cracking behavior of overlapping crack segments are obtained. A typical example is the complex deformation behavior in overlapping regions where pairs of crack segments partially overlap. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2009.05.004

Language：English   Publishing type：Research paper (scientific journal)  

Synchrotron X-ray microtomography was used to observe hydrogen micropores. Competitive growth between pre-existing high-density micropores and voids originating from damage during loading was observed in an aluminum alloy during a tensile test. Extensive and premature growth of pre-existing hydrogen micropores has been observed during tension. while the ordinary damage initiation increased rapidly more later. According to the estimation on the areal fraction of dimple patterns originating from the pre-existing hydrogen micropores, it has been concluded that the hydrogen micropores more or less make contributions to ordinary ductile fracture. [doi:10.2320/matertrans.M2009123]

DOI： 10.2320/matertrans.M2009123

Repository Public URL： http://hdl.handle.net/2324/4149933

Language：English   Publishing type：Research paper (scientific journal)  

The fatigue crack propagation process in an Al-Mg-Si alloy was investigated using in situ high-resolution synchrotron radiation Xray microtomography. Tomography datasets were obtained at periodic intervals throughout the 120,000 fatigue cycles. Three-dimensional rendering of the through-thickness crack shape indicates that in a number of regions the adjacent sides of two branched cracks tend to overlap with fatigue cycling and form a crack overlapping region. Measured crack growth rates in each tomographic slice show that crack growth retardation generally occurs in these crack overlapping regions. The through-thickness variation in crack tip opening displacement was also measured and was used to account for the observed crack propagation behavior. Crack morphologies were observed at different load levels in a fatigue cycle. The crack closure level varied for two selected regions comprising different overlapping cracks. The correlation of the crack growth rate with both crack opening and Closure levels was discussed and interpreted. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2009.03.036

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2464/jilm.59.312

Language：English   Publishing type：Research paper (scientific journal)  

X-ray microtomography was used to observe hydrogen micropores and thier growth behavior at high temperatures in several aluminium alloys. High-density micropores were observed in high-purity Al-Mg alloys, but their density and volume fraction were much lower in pure aluminum. Our results have revealed that the growth behaviour of micropores is dominated by Ostwald ripening. About 53&#37; of hydrogen is trapped in micropores in Al-Mg alloy with low hydrogen content, making micropores the predominant hydrogen trap site. Although total hydrogen content is similar to that in the alloy, the ratio of hydrogen trapped in micropores is below 7&#37; in pure aluminium. This difference is attributable to the lack of hydrogen precipitation sites in pure aluminium. Although the overall amounts of hydrogen at dislocations and grain boundaries are small in all the materials, the occupancies for these trap sites were concluded to be very high. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rigths reserved.

DOI： 10.1016/j.actamat.2009.01.026

Repository Public URL： http://hdl.handle.net/2324/1813034

Language：English   Publishing type：Research paper (scientific journal)  

Preliminary thermomechanical treatments (PTMTs) for age-hardening aluminuml alloys have been proposed to improve thermomechanical fatigue (TMF) resistance. Preferential orientation of precipitates perpendicular to the loading direction, achieved in advance by applying an out-of-phase PTMT with small temperature and strain ranges, call effectively prolong in-phase TMF life. This has been shown to correlate with the degree of preferential orientation due mechanical anisotropy introduced during PTMTs. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2008.11.005

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Synchrotron X-ray microtomography has been utilized for the ex-situ observation of micro-pore growth/annihilation behaviors of a 2024 aluminum alloy at a high temperature. High-resolution experimental configurations have enabled the 3D reconstruction of micro-pore and intermetallic compound particle images with isotropic voxels with 0.088-0.474 μm edges. The variations in micro-pore shape, size and spatial distribution at the high temperature are readily observed, with the tomographic volumes then being provided for the quantitative image analysis of such quantities. It has been clarified that micro-pores, that appear to be nucleated heterogeneously on particles, exhibit the Ostwald growth behavior during the high temperature exposure. Three-dimensional finite element meshes have been generated to monitor distributions of local stress and strain in real materials with such micro-pores. Since micro-pores tend to lie along (former) grain boundary, there seems to be some anisotropic effect on the strain redistribution due to the existence of micro-pores. Since local strain elevation is predicted by 50-200% in the vicinity of micro-pores aligned along grain boundary, it can be inferred that ductile fracture would be promoted considerable by the growth of pre-existing micro-pores.

DOI： 10.2464/jilm.59.30

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

X-ray microtomography has been utilized for the observation of ductile fractures in ail aluminum alloy with in Al/Al-Si dual phase Structure. A procedure for analyzing a series of tomographic images is proposed for extracting the variation in the local crack-tip opening displacement (CTOD), and its feasibility is confirmed. Complicated crack growth behavior and the formation Of uncracked ligaments ahead of a crack tip are observed in the alloy owing to the marked difference in local fracture toughness between the two phases. The proposed technique has provided a quantitative interpretation for such phenomena. It is clarified that a conventional measurement significantly overestimates the CTOD level. The transition behavior in CTOD has been revealed over a certain distance across an interface between the two phases, suggesting the existence of scaling effects that influence the microstructure/fracture relationship. Overall the current method could offer a highly effective way of assessing three-dimensional local fracture behavior. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2008.08.022

Language：English   Publishing type：Research paper (other academic)  

3D image analysis for evaluating internal deformation/fracture characteristics of materials

DOI： 10.1109/icpr.2008.4761648

Language：English   Publishing type：Research paper (scientific journal)  

In the past, all methods which understand deformation/fracture (D/F) characteristics have been limited on the surface indirectly. D/F characteristics are impacted by nano-scale structural features like air bubbles (pores); therefore, they need to be analyzed including inside. In this paper, we propose a system which automatically obtains the corresponding relations between pre- and post-D/F pores. Our system enabled analyzing three-dimensional, local, high-accuracy D/F characteristics.

DOI： 10.1002/ecj.1005

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2464/jilm.58.524

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

Change in microstructure of Al-Si-Cu casting alloys during high temperature solution treatment
The solution treatment in Al-Si system casting alloys is usually performed to obtain supersaturated solid solution and spheroidising Si particles. It can be inferred that a high temperature solution treatment enhances mechanical properties without any special apparatuses or techniques. However, it is well known that the solution treatment close to an eutectic temperature causes local melting. In this study, the change in microstructure of Al-Si-Cu casting alloys, which have been solution treated at temperatures ranging from 773 to 824 K, have been investigated from a viewpoint of Cu concentration and the distributions of micropores and locally melt regions due to eutectic reaction. Tensile and hardness tests were carried out to discuss the relationship between mechanical properties and microstructures. In addition to a surface observation, an internal microstructural observation was carried out using the high resolution X-ray computed tomography. The burnt regions during the high temperature solution treatment were identified to be Cu rich. Porosity increased with increasing the solution treatment temperature. The porosity in the sample solution treated above a binary eutectic temperature was confirmed to be >0.2 vol.-&#37;. The Cu concentration in the alpha-phase increased below the binary eutectic temperature.

DOI： 10.1179/136404608X361783

Language：English   Publishing type：Research paper (scientific journal)  

The literature contains many models for the process of void nucleation, growth and coalescence leading to ductile fracture. However, these models lack in-depth experimental validation, in part because void coalescence is difficult to capture experimentally. In this paper, an embedded array of holes is obtained by diffusion bonding a sheet filled with laser-drilled holes between two intact sheets. The experiments have been performed with both pure copper and Glideop. Using X-ray computed tomography, we show that void growth and coalescence (or linkage) are well captured in both materials. The Brown and Embury model for void coalescence underestimates coalescence strains due to constraining effects. However, both the Rice and Tracey model for void growth and the Thomason model for void coalescence give good predictions for copper samples when stress triaxiality is considered. The Thomason model, however, fails to predict coalescence for the Glidcop samples; this is primarily due to secondary void nucleation. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2008.02.027

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.msea.2007.11.007

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

The thermo-mechanical fatigue life and microstructural change under a compression-tension thermo-mechanical cyclic loading of a surface-hardened Al-Si-Mg alloy casting are investigated. A surface cold working technique using steel balls is utilized for the surface hardening. Out-of-phase type thermo-mechanical fatigue tests have been performed with the temperature range of 323-523K and the applied mechanical strain range of 0.75-2.0%. The surface-hardened material exhibits better thermo-mechanical fatigue property especially in a low cycle regime, together with higher generated stress, suggesting that it is even superior under stress-controlled loading. The differences in the stress-strain hysteresis loops and hardness variation near specimen surface between the materials with and without surface hardening have not vanished until final fracture. The observed difference in the thermo-mechanical property is attributed to some microstructural differences. The effects of damaging at the silicon particles to this difference are also investigated using the high-resolution microtomography technique. It has been clarified by microstructural observations that recovery and recrystallization are suppressed in the surface-hardened material. It can be inferred that such thermal stability is attributed to the multi-axial deformation by a combination of the surface hardening and the thermo-mechanical loading.

DOI： 10.2464/jilm.58.236

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Three-dimensional visualization of ductile fracture in an Al-Si alloy by high-resolution synchrotron X-ray microtomography
A direct three-dimensional visualization of the ductile fracture process under monotonic loading, in an Al-Si-Mg alloy specimen containing a fatigue pre-crack, has been conducted by means of the high-resolution X-ray computed tomography. Different morphology features of the crack viewed on different cross sections within the bulk of the specimen are detected. The isolated voids are distinguished from the microcracks. The evolution of the crack and voids as a function of the applied load are monitored and analyzed three-dimensionally. The advantages of the technique over traditional cross sectional observations are demonstrated, which facilitates to understand the fracture mechanisms in ductile materials, and to elucidate the fracture/microstructure interaction in non-uniform mediums. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2006.10.201

Language：English   Publishing type：Research paper (scientific journal)  

The three-dimensional (3-D) strain map is useful to elucidate the relationships between microstructures and locally caused deformation and fracture. However, a robust tracking method, which enables error-free tracking in synchrotron radiation computed tomography (SR-CT) images with >10 000 microstructural features, is not currently available. In this study, a model sample was subjected to a tensile test and scanned by the SR-CT technique in order to develop a new tracking method. The developed tracking methods indicated a high tracking ratio and tracking success ratio of nearly 100&#37; in a wide strain range, which included the assumed strain in a practical experiment. It was confirmed that tracking errors produce an incorrect strain distribution in 3-D strain mapping. This study verified the validity of the developed tracking method. The application of this method to high-resolution SR-CT images will make measurement and visualization of the strain distribution possible in three dimensions in bulk materials. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2007.12.058

Language：English   Publishing type：Research paper (scientific journal)  

The microstructure and hardness near the surface of a biomedical titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), subjected to gas nitriding at 1023-1223 K was investigated in comparison with the conventional biomedical Ti-6Al-4V ELI (Ti64). After gas nitriding, the microstructure near the specimen surface was observed by optical microscopy, X-ray diffraction (XRD), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). In both alloys, two types of titanium nitrides (TiN and Ti(2)N) are formed and the a phase is precipitated by gas nitriding. Furthermore, the oxygen impurity in the gas nitriding atmosphere reacts with the titanium nitrides; thus, TiO(2) is formed at the outermost titanium nitride layer. The surface hardening was also evaluated by Vickers hardness measurement. The Vickers hardness near the surface of TNTZ and Ti64 increases significantly by gas nitriding. (c) 2007 Published by Elsevier B.V.

DOI： 10.1016/j.msea.2007.08.065

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

We present a combined novel methodology to study the three-dimensional complex geometry of a tortuous crack and identify the essential features of the crack and its propagation inside a heterogeneous material. We find that some severe damage events occur unexpectedly below a local mode-I crack within the sample; we realize that the severe plastic zone of the local mode-I crack is shifted down by another unseen crack segment hidden behind, which is responsible for the unusual damage phenomenon observed. We also find that the crack grows fast at some locations but slowly at some other locations along the crack front; we recognize that the crack-tip fields are reduced by neighboring hidden crack segments, which accounts for the retarded propagation of some part of the crack front. The feasibility and power of the proposed methodology highlights the potential of a new way to study fracture mechanisms in real materials.

DOI： 10.1103/PhysRevLett.100.115505

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Synchrotron X-ray microtomography has been utilized for the in-situ observation of ductile fracture in cast Al-7%Si alloys exposed at a high temperature for 0-10⁶ s. A high resolution experimental configuration and deflection contrast imaging technique have enabled the reconstruction of silicon particle images with an isotropic voxel with a 0.474 μm edge. The variations in particle shape, size and spatial distribution at the high temperature are readily observed, along with the existence and growth of high-density micro-pores. Three-dimensional image analysis is applied and its feasibility is confirmed. It is clarified that in the case of an as-cast material void nucleation and growth have been observed as has been reported for the general ductile fracture of metallic materials. When it is exposure at the high temperature for a long time, however, ductile fracture is found to be attributable mainly to the growth of pre-existing micro-pores and not the nucleation of new voids at silicon particles. Since such tendency has been also confirmed for other materials, more detailed analysis might be expected in a near future in order to understand actual ductile fracture process in practical materials.

DOI： 10.2464/jilm.58.58

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

Synchrotron radiation x-ray microtomography is becoming a uniquely powerful method to nondestructively access three-dimensional internal microstructure in biological and engineering materials, with a resolution of 1 mu m or less. The tiny field of view of the detector, however, requires that the sample has to be strictly small, which would limit the practical applications of the method such as in situ experiments. In this paper, a wavelet-based local tomography algorithm is proposed to recover a small region of interest inside a large object only using the local projections, which is motivated by the localization property of wavelet transform. Local tomography experiment for an Al-Cu alloy is carried out at SPring-8, the third-generation synchrotron radiation facility in Japan. The proposed method readily enables the high-resolution observation for a large specimen, by which the applicability of the current microtomography would be promoted to a large extent. (C) 2007 American Institute of Physics.

DOI： 10.1063/1.2818374

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

The effect of the flow-forming process on the fatigue behavior of an Al-Si-Mg alloy was investigated using synchrotron X-ray microtomography. The fatigue life of the flow-formed-T6 specimen was found to be longer than that of the as-cast-T6 in all the selected stress amplitudes. The X-ray-scanned radiographs of a flow-formed-T6 specimen were reconstructed to allow three-dimensional (3-D) visualization of distribution of micropores and pore-crack interactions. Observations were performed on different tomographic slices to investigate the interaction between the micropores and the crack. Micropores have been associated with deflections of the crack path. Mode I and Mode 11 stress-intensity factors (SIFs) were calculated at each position along the fatigue-crack path using a micromechanics model. The SIF increased rapidly when the fatigue crack came close to a micropore. It was found that the average value of SIFs along entire crack paths was slightly higher than the remotely applied stress intensity, although the level of antishielding was pronounced in some local regions. Crystallographic texture is proposed to be the important factor for the observed higher fatigue resistance in flow-formed-T6 material.

DOI： 10.1007/s11661-007-9214-6

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

Understanding the mechanism of fatigue crack propagation in bones is important because fatigue is probably the main cause of clinical stress fractures. Here, fatigue crack initiation and propagation behaviors of bovine humerus and femur regarding microstructures were investigated by the replica method. Fatigue tests were conducted to obtain SN curves of these compact bones. Both these bones are made up of haversian and plexiform, bones, classified by their microstructures. The crack propagation rate is faster when the microstructure is inclined to the bone axis than when parallel. The fatigue strength of plexiform bone is higher than that of haversian bone. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijfatigue.2006.09.018

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

The local elastic and plastic strain during deformation are very complicated and different form the macroscopic strain, because most materials have inhomogeneous microstructure. In this study, local strain distribution in three dimensions has been measured using the new developed method based on image analysis in high-resolution synchrotron radiation computed tomography (SR-CT). Model and practical specimens, which made of cupper alloy and aluminum alloy, respectively, were prepared for a development procedure and application of local strain measurements. Gauging intervals of microstructural features before and after deformation gave us information of inhomogeneous local strain distribution in three dimensions. High strain was observed in a necking region appeared after tensile deformation in the model sample. A combination of non-destructive measurements by SR-CT and three-dimensional analysis revealed inhomogeneous strain distributions in practical aluminum samples.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Formation of the reaction product layer on the surface of biomedical titanium alloys, Ti-29Nb-13Ta-4.6Zr (TNTZ) and Ti6A1-4V ELI (Ti64), during gas nitriding was investigated. These alloys were exposed to nitrogen atmosphere at 1023, 1073, 1123 and 1223 K. After the gas nitriding, a reaction product layer was observed on the surface of both alloys, and was analyzed using an X-ray diffraction (XRD), Auger electron spectroscopy (AES) and X-ray Photoelectron spectroscopy (XPS). The layer was comprised of two phases, which were outer oxide layer (mainly Ti02) and inner nitride layer (mainly TiN or Ti ₂N). In these layers, the thickness of the oxide layer particularly depended on the kinds of alloys. According to the thermodynamics and point defect theory, the growth rate of oxide layer is expected to be increased by the presence of Al in TiO₂. Namely, the dissolution of Al into TiO ₂ may increase the number of oxygen vacancies, resulting in acceleration of oxygen diffusion inward. On the other hand, the elements that accelerate the growth of the oxide layer are not contained in TNTZ. Thus, the oxide layer formed on Ti64 was thicker than that of TNTZ. In a similar way, the elements that accelerate the growth of the nitride layer are not contained in both TNTZ and Ti64. Thus, the nitride layers with similar thicknesses may be formed on TNTZ and Ti64 during gas nitriding.

DOI： 10.2320/jinstmet.71.415

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

The present authors have proposed in-situ composites in which cold working was applied to the cutting chip mixture of dissimilar materials. The composites have exhibited superior strength together with ultra-fine grain structure. In this study, such composite materials are produced by combining 6061 aluminum alloy and IF steel chips. Microstructural evolution processes are visualized by means of the microtomography as well as the TEM observation. It has been clarified that ultra-fine grains with a large fraction of high angle boundaries are obtained due to the effects of severe plastic deformation during cutting. Grain size of the matrix aluminum alloy is reduced to about 220 nm by applying swaging strain of only 1.9. It should be noted that the significant strain hardening of the chips occurs during initial deformation stage where strain applied by swaging seems to be consumed mostly for consolidation. The chips gradually change their orientation in the material at this stage. It can be inferred that the rapid development of ultra-fine structure in the matrix is also attributed to gradual change in deformation axis thereby realizing effective multi-axial deformation. Overall, the utilization of chips is identified as a highly effective way of grain refining compared to the other uni- and multi-axial deformation processes.

DOI： 10.2320/jinstmet.71.368

Language：English   Publishing type：Research paper (scientific journal)  

The microstructural change during a compression-tension thermomechanical cyclic loading of an Al-Si-Cu-Mg alloy casting is investigated. Although the thermomechanical fatigue loading was applied after the alloy was tempered to the T6 peak aging condition, preferential orientation of precipitates is observed together with anisotropy in deformation behavior. The precipitates are observed to align perpendicular to a compressive stress during heating. The effects of preferential orientation are also discussed on the basis of a model analysis. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2006.11.005

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Measurement of interior strain distribution has been developed based on the synchrotron radiation computed tomography (SR-CT). In metal deformation, local strain distribution differs from macroscopic strain due to microstructural factors such as grains, grain boundaries, particles, pores, voids, and cracks. A model sample, which was made from a copper alloy strengthened with alumina, was prepared containing artificial pores. Tensile loading was applied to the sample step by step. High-resolution tomographic experiment was performed at the third-generation synchrotron radiation facility (SPring-8) in Japan. Gravity center position, volume and surface area in the pores, which were regarded as markers in a tracking procedure, were measured by 3-D digital image analysis in the SR-CT images. The markers before and after the deformation were provided for registration and macroscopic strain correction before the tracking procedure. The marker tracking was carried out by means of matching parameter that was described as functions of distance, volume and surface at markers. The ratio of success tracking was evaluated in order to clarify whether the tracking method developed in this study was reliable. The 3-D strain distribution was represented successfully by the tracking results. A combination of high-resolution SR-CT and tracking of microstructural features is effective to visualize interior strain distribution in materials in 3-D.

DOI： 10.2320/jinstmet.71.181

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

In the past, all methods which understand deformation / fracture (D/F) characteristics have been limited on the surface indirectly. D/F characteristics are impacted by nano-scale structural features like air bubbles (pores); therefore, they need to be analyzed including inside. In this paper, we propose a system which automatically obtains the corresponding relations between pre- and post-D/F pores. Our system enabled analyzing three dimensional, local, high-accuracy D/F characteristics.

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

In this article, a new concept of smart coating is presented, which enables failure prevention under thermo-mechanical fatigue loading by a simple coating without using any external devices. The feasibility of arresting fatigue crack propagation under thermo-mechanical loading is experimentally demonstrated for an Al-Si practical casting alloy by applying a simple and inexpensive coating prior to usage. An Sn alloy has been chosen as a coating material as a result of extensive screening tests. Valuable mechanistic insight has been gained from numerical simulation indicating that the crack driving force can be reduced by the crack closure mechanism induced by the impregnation of coating material.

DOI： 10.1177/1045389X06065235

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

Microtomography combined with hard x-ray imaging microscopy has been employed to observe nanoscopic features in a material, which has, to date, only been done by the transmission electron microscopy (TEM). Here, the authors show a characteristic microstructure in an aluminum alloy, such as a slant gap between growing precipitates that impinge on each other due to the presence of a solute-depleted zone. Such observation is not possible by conventional projection microtomography even using the highest resolution available. It would appear that the present technique has a unique potential to observe nanoscopic features inside materials that are several orders of magnitude thicker than TEM specimens. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2359288

Language：English   Publishing type：Research paper (scientific journal)  

Experimental and numerical investigations of the effects of the spatial distribution of alpha phase on fracture behavior in hypoeutectic Al-Si alloys
A uniform, fine a phase microstructure enhances the mechanical properties of Al-Si alloys; however, it is an open question as to how the alpha phase affects the crack growth behavior. This paper addresses the effects of the morphology and distribution of alpha phase on the fracture behavior in a model dual-phase Al-7&#37; Si alloy with different microstructures. The influences of microstructural factors on crack growth behavior are examined using in situ experiments. The results show that a globular alpha phase microstructure produces a straight crack growth path, whereas a dendritic, orientational alpha phase microstructure leads to a deflected crack profile. Finite-element modeling is performed to simulate the fracture behavior, and to rationalize the observed phenomena. The near-tip J-integral-based fracture criterion is used to predict the fracture path. Numerical results indicate that a variation in the morphology and distribution of alpha phase changes the symmetry and intensity of the near-tip stress, strain and displacement fields due to the strong mismatch in elastic plastic properties of the a phase and eutectic phase, which have major influences on both crack growth direction and crack tip driving force. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2006.06.036

Language：English   Publishing type：Research paper (scientific journal)  

The preferential penetration of a liquid metal along grain boundaries (GBs) in polycrystalline metals is a well-known phenomenon. Gallium-decorated GB networks in rolled aluminium alloys have been visualized three-dimensionally using the high-resolution synchrotron radiation computer tomography (SRCT). The distribution of gallium concentration along GBs was measured using X-ray absorption. Statistical correction for blurring was performed to raise accuracy of the measurement, and then compared with orientation mapping by the SEM/EBSP method on the surface of a tomographic specimen. The pancake-like grain microstructure formed by a rolling process causes the anisotropy of penetration direction. Although the gallium penetrated into high-angle GBs, all of the high-angle GBs are not necessarily decorated by the gallium. The reason for this may be explained by considering geometrically possible penetration paths that seem to be dependent on local grain arrangement and GB structure through each path. The dependence of the gallium concentration on the rotation axis of misorientation has been found along the high-angle GBs. Especially, GBs with a specific misorientation (< 221 > as a misorientation axis) showed high gallium concentration.

DOI： 10.1080/14786430600710933

Language：English   Publishing type：Research paper (scientific journal)  

We have investigated the compressive behaviour of closed-cell aluminium foams using a high-resolution X-ray CT. The microstructures of cell walls or Plateau borders in the foams were visualized in 3D using the local tomography technique which is a high-resolution CT method to reconstruct a region of interest within a large sample. The shapes and the 3D distribution of micropores, particles, and regions of solute segregation in the foams are evaluated, comparing the cell walls with the Plateau borders. Under compressive loads, the damage behaviour of such microstructures has been observed using an in situ test rig. It is found that the microcracks were mainly initiated from the cell walls and the micropores with large diameters were also damaged. The crack initiation sites are classified from the results. In addition, a method for non-destructive characterization of elastic and plastic deformation in the foams, which is called a 3D microstructure gauge (MG) method, is presented. Thousands of micropores as markers on each load were automatically matched by the information of those volumes and surface areas. The local strain mapping by the MG indicates that the edges of the micropores with large diameters have large strain under compression and this is consistent with the crack analyses.

DOI： 10.1080/14786430600724454

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Quantitative assessment of liquid Ga penetration into an aluminium alloy by high-resolution X-ray tomography
We have evaluated the liquid Ga penetration into an aluminium alloy by high-resolution X-ray tomography. The 3D visualization of a crack together with its surrounding grain structure was per-formed with the help of the Ga penetration technique. It is found that the advance directions of the crack-tip were strongly influenced by the grain microstructure and the branching of the crack is affected by grain distribution. In this study, the liquid Ga not only acts as a contrast agent for grain boundaries, but also expands the volume of the Al alloy due to Ga diffusion and associated processes. The 3D strain between the grains has been determined by microstructural gauging technique, which uses micropores as marker points. The 3D expansion of the sample volume, the volume reduction of micropores and the brittle fracture were evidently observed. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2005.06.045

Language：English   Publishing type：Research paper (scientific journal)  

We have evaluated the liquid Ga penetration into an aluminium alloy by high-resolution X-ray tomography. The 3D visualization of a crack together with its surrounding grain structure was performed with the help of the Ga penetration technique. It is found that the advance directions of the crack-tip were strongly influenced by the grain microstructure and the branching of the crack is affected by grain distribution. In this study, the liquid Ga not only acts as a contrast agent for grain boundaries, but also expands the volume of the Al alloy due to Ga diffusion and associated processes. The 3D strain between the grains has been determined by microstructural gauging technique, which uses micropores as marker points. The 3D expansion of the sample volume, the volume reduction of micropores, and the brittle fracture were evidently observed. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2005.07.050

Language：English   Publishing type：Research paper (scientific journal)  

Ti-XNb-10Ta-5Zr alloys were fabricated based on Ti-30Nb-10Ta-5Zr alloy, which was the composition that simplified that of Ti-29Nb-13Ta-4.6Zr alloy for biomedical applications. The tensile deformation mechanisms of the Ti-25Nb-10Ta-5Zr, Ti-30Nb-10Ta-5Zr, and Ti-35Nb-10Ta-5Zr alloys were investigated using X-ray diffraction analysis under several loading conditions. Under loading conditions, the X-ray diffraction peaks of all specimens in this study shift to higher angles than those obtained under non-loading conditions. In the crystal orientation of Ti-30Nb-10Ta-5Zr alloy, in which the lattice strain has reached the maximum elastic lattice strain, plastic deformation (for example slip) is moved with elastic deformation. Therefore, the elastic modulus of this alloy appears to decrease in terms of strain over a proportional limit. Thus, the elastic deformation behavior of the Ti-30Nb-10Ta-5Zr alloy does not obey Hooke's law.

DOI： 10.2320/jinstmet.70.572

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

3-D image-based mechanical simulation of aluminium foams: Effects of internal microstructure
SR (Synchrotron radiation) X-ray microtomography has been utilized for the 3D characterization of microstructures in an aluminium foam. Volume tomographic data sets are converted into stereolithography tessellation language (STL) models to create 3-D finite-element simulation models. Both quasi-static and dynamic deformation and damage behaviours are investigated numerically, especially focussing on the effects of relatively small micro-pores inside cell wall materials. It has been fairly obvious that the existence of micro-pores and their spatial distribution pattern in cell materials would be a key issue to control the deformation and fracture behaviours. It has been also clarified that the stress wave propagation during the dynamic loading is prone to relatively uniform local stress elevation compared to the case of the static compression, thereby more extensive damage is predicted in the case of the dynamic loading due to the increase in volume sampled by an external loading. These results are in qualitative agreement with experimental observations. Overall, the approach taken in this study has provided highly effective ways to characterize microstructure/properties relationships in such highly heterogeneous materials.

DOI： 10.1002/adem.200600035

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DOI： 10.1002/adem.200600034

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/adem.200600039

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Synchrotron X-ray microtomography has been used for the three-dimensional characterization of microstructure in the cell walls of aluminum foams. A combination of high-resolution phase contrast imaging technique and several application techniques has enabled the quantitative image analyses of microstructures as well as the assessment of their effects on deformation behaviors. The application techniques include local area tomography, microstructural gauging and in-situ observation using a specially desioned material test rig. It has been clarified that ductile buckling of a cell wall occurs regardless of any of the microstructural factors in the case of a pure aluminum foam, while rather brittle fracture of a cell wall is induced by the existence of coarse micropores and their distribution independently of the intermetallic particles and the grain boundary in the case of aluminum foams alloyed with Zn and Mg. It has also been confirmed that coarse TiH2 particles, which are a residual foaming agent added to alloy melts, remain intact during the deformation. When cooling rate during foaming is high, however, lower energy absorption might be attributable to the significant amount of residual TiH2 particle and its inhomogeneous distribution. These tendencies are also confirmed by three-dimensional strain mapping by tracking internal microstructural features.

DOI： 10.1007/s11661-006-1072-0

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An understanding of how fatigue cracks propagate in the bone is important because fatigue is thought to be the main cause of clinical stress fractures. In this study, fatigue crack initiation and propagation behaviors of bovine humerus and femur were investigated with respect to their microstructures. The initiation and propagation of fatigue cracks were observed in a specimen surface by using the replica method. Fatigue tests were also conducted on the bovine humeral and femoral compact bones in order to obtain S-N curves. Based on their microstructures, the bovine humeral and femoral compact bones are classified into the haversian and plexiform bones. In haversian bone, when the microstructure is inclined toward the bone axis, the fatigue crack initiates at the osteon-ossein interface and osteon lamellae interface. In case the microstructure is parallel to the bone axis, the fatigue cracks initiate at the haversian canals, Volkmann's canals, osteon-lamellae interface, and osteon-ossein interface. Among these, the fatigue crack that initiates at the Volkmann's canal may receive a relatively greater maximum shear stress; therefore, it has a tendency to be the main propagating fatigue crack that connects the fatigue cracks initiated at the other above mentioned sites. In the plexiform bone, when the microstructure is inclined toward the bone axis, fatigue crack initiates at the interface of the lamellae. When the microstructure is parallel to the bone axis, fatigue cracks initiate at the blood vessel and interface of the lamellae. The fatigue crack that initiates at the blood vessel may receive a relatively greater maximum shear stress; therefore, it has a tendency to be the main propagating fatigue crack that connects the fatigue crack initiated at the other site. In the haversian and plexiform bones, the crack propagation rate when the microstructure is inclined toward the bone axis is greater than that when the micro-structure is parallel to the bone axis.

DOI： 10.2320/jinstmet.70.350

Language：English   Publishing type：Research paper (scientific journal)  

The relationships between mechanical properties and microstructure of Ti-29Nb-13Ta-4.6Zr in under aged, peak aged and over aged conditions at various aging temperatures were investigated. The maximum Vickers hardness values of Ti-29Nb-13Ta-4.6Zr aged at 573 K, 673 K and 723 K are obtained at aging times of around 2419.2 ks, 3024 ks and 1209.6 ks, respectively. ω phase precipitates in β phase of Ti-29Nb-13Ta-4.6Zr at relatively low aging temperature, 573 K, while a phase precipitates in β phase of Ti-29Nb-13Ta-4.6Zr at relatively higher aging temperature, 723 K. At an aging temperature of 673 K that lies between aging temperatures of 573 K and 723 K, ω phase precipitates at the early stage of aging, but a phase precipitates at relatively longer aging time. The precipitation site of a phase changes from intragrain to grain boundary at around peak aging time when Ti-29Nb-13Ta-4.6Zr is aged at 673 K and 723 K. The tensile strength of Ti-29Nb-13Ta-4.6Zr aged at 573 K, 673 K and 723 K increases up to a peak aging time with increasing aging time, but under over aging conditions, the tensile strength decreases. While the elongation decreases with increasing aging time at every aging temperature. The fatigue strength of Ti-29Nb-13Ta-4.6Zr increases greater when α phase precipitates than when ω phase precipitates. The fatigue strength of Ti-29Nb-13Ta-4.6Zr decreases a little due to the coarsening of α phase precipitated in β grain.

DOI： 10.2320/jinstmet.70.295

Language：English   Publishing type：Research paper (scientific journal)  

In order to produce a novel bioactive beta-type titanium alloy -Ti-29Nb-13Ta-4.6Zr - and pure titanium for biomedical applications, an electrochemical treatment involving anodic oxidizing and cathodic polarization was applied to the alloy in calcium nitrate solution under various conditions. For creating a hydroxyapatite (HAP) coating on the alloy, the treated alloy and pure titanium were dipped into simulated body fluid (SBF) and then into 1.5SBF, wherein the concentration of constituents was 1.5 times that of SBF. The characterization and morphology of HAP formed on the alloy were examined in comparison with those of pure titanium. In Ti-29Nb-13Ta-4.6Zr, the formability of HAP in SBF after the electrochemical treatment is less than that in pure titanium. The thickness of a calcium hydroxide layer formed by the cathodic polarization can be controlled by the cathodic potential. In both pure titanium and Ti-29Nb-13Ta-4.6Zr, the formability of HAP increases up to a certain increase in the thickness of the oxide layer formed by the anodic oxidizing. Therefore, the formability of HAP decreases due to a reduction in the formability of the calcium hydroxide layer. The number of hydroxyl groups on the surface of Ti-29Nb-13Ta-4.6Zr is less than that in pure titanium after the anodic oxidizing. The tensile bonding strength of HAP in Ti-29Nb-13Ta-4.6Zr is similar to that in pure titanium.

DOI： 10.2320/jinstmet.70.304

Language：English   Publishing type：Research paper (scientific journal)  

In recent years, the opportunity of the hard tissues such as bones, hip joints and tooth to be replaced by metallic biomaterials is increasing. In general, metallic biomaterials lack bioactivity, which is the ability to directly form a chemical bond with bones. Therefore, the bioactive surface modifications on surface of metallic biomaterials have been investigated and applied. Among them, the calcium phosphate invert glass coating method, which is dip-coating treatment (DCT), can be granted the bioactivity on the surface of β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy, for biomaterial applications. In this study, aging characteristics and mechanical properties of TNTZ alloy surface-modified with DCT were investigated. There is an oxide layer and a case near boundary between calcium phosphate invert glass layer and TNTZ surface in TNTZ surface-modified with DCT (TNTZ _DCT). A very fine ω phase precipitates in an equiaxed β phase with an average diameter of 20 μm at a distance of 200 μm from specimen surface. On the other hand, the microstructure of aged TNTZ _DCT has an α phase. The tensile strength of TNTZ _DCT is around 30% greater than that of as-solutionized TNTZ (TNTZ _ST). On the other hand, the elongation is around 48% smaller than that of TNTZ _ST. Tensile strength of aged TNTZ _DCT is around 26% greater than that of TNTZ _DCT. While the elongation of aged TNTZ _DCT is around 52% smaller than that of TNTZ _DCT. Fatigue limit of TNTZ _DCT is nearly equal to that of TNTZ _ST. Fatigue limit of aged TNTZ _DCT is around 80 MPa greater than that of TNTZ _ST. Fatigue limits of TNTZ _DCT and aged TNTZ _DCT, where their fatigue specimen surfaces are mirror-polished, rise as compared with those of TNTZ _DCT and aged TNTZ _DCT, where their fagigue specimen surfaces are shot-blasted.

DOI： 10.2320/jinstmet.70.314

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Ti-30Nb-10Ta-XZr alloys were fabricated based on Ti-30Nb-10Ta-5Zr alloy, which was the composition simplified that of Ti-29Nb-13Ta-4.6Zr alloy for biomedical applications. The tensile deformation mechanisms of Ti-30Nb-10Ta-XZr alloys (X: 0, 3, 5, 7 and 10%) were then investigated. The plastic deformation mechanisms of Ti-30Nb-10Ta-XZr alloys during tensile loading change with changing Zr content. Microstructure of Ti-30Nb-10Ta alloy without Zr after tensile test shows a stress-induced transformation of β phase. In Ti-30Nb-10Ta alloy, the plastic deformation mechanism is mainly dominated by the stress-induced transformation of β phase. Microstructure of Ti-30Nb-10Ta-3Zr alloy after tensile test shows a stress-induced transformation of β phase and many dislocations in β phase. In Ti-30Nb-10Ta-3Zr alloy, the plastic deformation mechanism is mainly dominated by the stress-induced transformation of β phase and slip. Microstructures of Ti-30Nb-10Ta-XZr alloys (X: 5, 7 or 10%) after tensile test show many dislocations in β phase. In these alloys, the plastic deformation mechanisms are mainly dominated by slip. The elastic deformations of Ti-30Nb-10Ta-XZr alloys (X: 3, 5 or 7%) do not depend on Hooke's law. The maximum recovery strains of these alloys increase with increasing the total strain.

DOI： 10.2320/jinstmet.70.89

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In this paper, several widely applied fracture criteria were first numerically examined and the crack-tip-region J-integral criterion was confirmed to be more applicable to predict fracture angle in an elastic-plastic multiphase material. Then, the crack propagation in an idealized dendritic two-phase Al-7&#37;Si alloy was modeled using an elastic-plastic finite element method. The variation of crack growth driving force with crack extension was also demonstrated. It is found that the crack path is significantly influenced by the presence of a-phase near the crack tip, and the crack growth driving force varies drastically from place to place. Lastly, the simulated fracture path in the two-phase model alloy was compared with the experimentally observed fracture path.

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The effect of loading rate on absorbed energy and fracture surface area of three types of wrought aluminum alloys, namely high toughness 5083-O and 6061-T651 alloys and low toughness 7075-T6 alloy are studied. A laser displacement measuring equipment and a scanning laser microscope are used in order to measure three-dimensional geometry of the fracture surface. Shear lip and plastic hinge can be observed in 5083-O and 6061-T651 aluminum alloys. According to a measuring region, the calibration factor K is notably different. Moreover, the calibrated fracture surface area of each fracture geometry changes considerably with increasing loading rate. On the other hand, in 7075-T6 aluminum alloy, macroscopic fracture geometries are not clearly defined, and almost no difference appears in the calibration factor K within the same fracture surface. Moreover, calibrated whole surface area increases linearly with increasing loading rate. In any aluminum alloys, the tends in the loading rate change of calibrated whole fracture surface area, A _W, and the total absorbed energy, E _t, with loading rate are similar each other. Therefore, the change of fracture surface area is one of the main factors that affect the change of absorbed energy.

DOI： 10.2464/jilm.56.15

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Microstructure and fretting fatigue characteristics of highly workable titanium alloy with equiaxed α and Widmanstärten α structure

DOI： 10.2464/jilm.55.654

Language：Japanese   Publishing type：Research paper (scientific journal)  

Contact pressure and fretting fatigue characteristics of highly workable titanium alloy with equiaxed α and Widmanstätten α structure

DOI： 10.2464/jilm.55.661

Language：English   Publishing type：Research paper (scientific journal)  

The in situ high-resolution synchrotron x-ray computed microtomography has been applied to visualize and quantify the ductile fracture process of a notched Al alloy specimen. The three-dimensional (3D) investigation reveals that voids are nucleated, grow and coalesce more easily near the notch front and in the central region of the sample. These voids are mainly associated with Si particles in the eutectic (EU) phase. The 3D packing architecture of particles in the EU region, and the 3D morphology of alpha phase are also visualized. The feasibility of this technique highlights the potential of its application in the field of micromechanics-based fracture. (c) 2005 American Institute of Physics.

DOI： 10.1063/1.214208

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Hypoeutectic Al-Si alloys consist of primary alpha-Al and Al-Si eutectic phases and show typical elastic-plastic fracture. To understand their fracture behavior, fracture processes were simulated using an elastic-plastic finite-element method. The validity of the J-integral-based criterion was verified and applied to the simulations. A complicated model was used to simulate the fracture in an idealized dendritic microstructure, and four simplified models were intended to more clearly understand the interaction between a crack and individual alpha phases. Results show that the crack is attracted to the soft alpha phase when passing by the alpha phase, whereas it is repelled when the alpha phase is close in front of or behind the crack tip. The presence of alpha phase close in front of or behind the crack tip leads to an amplification of the driving force. However, the alpha phase beside the tip reduces the driving force. Furthermore, the fracture behavior is mainly affected by the adjacent alpha phase on one side around the crack tip, while the remote alpha phase on the opposite side has an offsetting effect. The local stress-strain fields were examined to analyze the simulated behavior. The simulated crack-growth path in the dendritic model was compared and verified with the experimentally observed path.

DOI： 10.1007/s11661-005-0071-x

Language：English   Publishing type：Research paper (scientific journal)  

The effects of microstructures on notch fatigue propertes of a Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) subjected to various thermo-mechanical treatments were investigated in this study. The notch fatigue strengths of TNTZ subjected to aging at 673 K and 723 K after solution treatment or cold rolling at stress concentration factors of 1 (without the notch), 2 and 6 in both low and high cycle fatigue life regions are greater than those of as-cold rolled and as-solutionized TNTZ, and TNTZ subjected to aging at 598 K after solution treatment or cold rolling. A single fatigue crack initiates on a specimen surface and at the tip of the notch at stress concentration factors of 1 and 2. While, a few cracks initiate the tip of the notch having a stress concentration factor of 6. Notch sensitivity factor of TNTZ is almost equal to or smaller than those of other materials such as Ti-6Al-4V, CP-Ti, S35C, S45C and SUS304. It is considered that the notch sensitivity factor decreases with decreasing the width of lath like α phase and its volume fraction.

DOI： 10.2464/jilm.55.575

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Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

It has been reported that nano-scale multifilamentary microstructure, which has been readily available in Al-Nb systems, was hardly realized in Al-Fe heavily-deformed composites systems. In the present study, state-of-the-art techniques are applied to gain basic insight into the necessary requirement for the texture development of the Al-Fe composites. Three-dimensional finite element meshes were generated to monitor local stress and strain distributions in real materials. The approach taken in this study may be characterized as ne,v type of the reverse engineering which is based on the visualization of microstructural features of materials. It has been clarified that local stress elevation occurs where the Fe phase is constricted or gnarled with flection when cutting chips are used as a matrix. Hydrostatic stress varies significantly in the Fe phase thereby promoting the plasticity of the Fe phase. Both sufficient strengthening of aluminum and irregular distribution of the embedded Fe phase are identified essential for multifilamentary microstructure formation.

DOI： 10.2320/matertrans.46.2229

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Despite its clinical importance in developing artificial bone, limited information is available regarding the microstructure with respect to the fatigue characteristics of bones. In this study, the fatigue characteristics of the bovine humerus and femur were investigated with respect to microstructures. Fatigue tests were conducted on the bovine humerus and femur at a stress ratio of 0.1 and a frequency of 10 Hz. The fatigue strength of the plexiform bone is slightly greater than that of the haversian bone. This is because the volume fraction of voids in the haversian bone, which is the site of stress concentration, is higher than that of voids in the plexiform bone. Several microcracks are observed on the fatigue fracture surface of the haversian bone. The microcracks are short and their propagation directions are random. However, the number of the microcracks in the plexiform bone is very small. The microcracks are relatively long and their propagation directions are parallel to the longitudinal direction of the lamellar bone. Therefore, the crack requires relatively more energy to propagate across the lamella in the plexiform bone.

DOI： 10.1299/jsmea.48.472

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Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Tensile and fatigue properties are important mechanical properties in drawn wires for biomedical and dental applications because of the credibility against the monotonic loading fracture or fatigue failure. The mechanical properties and deformation behavior of drawn wires of Ti-29Nb-13Ta-4.6Zr with diameters of 1.0 mm and 0.3 mm (designated as TNTZ _d1.0 and TNTZ _d0.3) were investigated to know a potential for biomedical and dental applications in this paper. The microstructure of forged Ti-29Nb-13Ta-4.6Zr subjected to a solution treatment at 1063 K (TNTZ _ST) comprises a single β phase with an average diameter of 25 μm. While that of TNTZ _d1.0 comprises a needle-like single β phase elongated parallel to the drawing direction. Tensile strengths of TNTZ _d1.0 and TNTZ _d0.3 are approximately 740 MPa and 800 MPa, respectively. While both elongations are nearly equal to each other (approximately 5.0%). The elastic modulus of TNTZ _d1.0 is approximately 50 GPa and that slightly smaller than approximately 55 GPa of TNTZ _d0.3. The notch-fatigue limit of TNTZ _d1.0 is 250 MPa. TNTZ _ST exhibits the maximum elastic strain of approximately 1.4%. And the stress-strain curve shows a single gradient during elastic deformation region. The stress-strain curves of TNTZ _d1.0 and TNTZ _d0.3 in the elastic deformation region show two gradients, and the values of the maximum elastic strains in both wires are approximately 2.9% and 2.8%, respectively.

DOI： 10.2320/jinstmet.69.530

Language：English   Publishing type：Research paper (scientific journal)  

The presence of calcium phosphate invert glass-ceramic (designated as CPIG) layer on the surface of artificial implant products can improve the bonding between these products and bones.
In this study, the morphology of the CPIG layer on the surface of a beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), was investigated for biomaterial applications by a dip-coating treatment. Furthermore, the mechanical properties of TNTZ coated with the CPIG layer were also investigated.
In the CPIG layer, a compositionally gradient zone with a thickness of approximately 2.0 mu m exists on the surface of the TNTZ. The titanium concentration in the zone increases with the decreasing distance from the CPIG surface toward the base materials. On the other hand, calcium and phosphorus concentrations in the zone increase with the distance from the TNTZ surface. The tensile bonding strength between TNTZ and the CPIG layer is 25 MPa and that between aged TNTZ and the CPIG layer is 18.6 MPa.
For easily understanding the change in mechanical properties by a dip-coating treatment, the values of those on TNTZ and TNTZ coated with CPIG layer were shown as follows. The tensile strength increases remarkably by a dip-coating treatment as compared with that of assolutionized TNTZ while the elongation is a reverse trend. Young's modulus of TNTZ and aged TNTZ coated with the CPIG increases by 15 to 27 GPa after the dip-coating treatment as compared with that of as-solutionized TNTZ (approximately 60 GPa). The fatigue limit of TNTZ coated with the CPIG layer is nearly equal to that (approximately 300 MPa) of as-solutionized TNTZ. On the other hand, the fatigue limit of aged TNTZ coated with the CPIG layer is a 100 MPa higher than that of as-solutionized TNTZ.

DOI： 10.2320/matertrans.46.1564

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Fatigue characteristics of low cost beta titanium alloys for healthcare and medical applications
Two new low cost beta titanium alloys, Ti-4.317e-7.1 Cr (TFC alloy) and Ti-43Fe-7. 1Cr-3.0Al (TFCA alloy) for healthcare and medical applications have been recently developed. As for such applications, the alloys are necessary to have high fatigue performance. The aim of this study is, therefore, to investigate fatigue characteristics of the alloys subjected to solution treatment above beta transus.
Fatigue tests were carried out at a stress ratio, R, of 0.1 and a frequency of 10 Hz. Fatigue limit of the solution treated TFC alloy is higher than that of the solution treated TFCA alloy, but both are higher than that of the existing biometallic materials. Fatigue strength of the TFC alloy is almost independent of solution treatment temperature, while, fatigue strength of the TFCA alloy strongly depends on solution treatment temperature, especially, in the low cycle fatigue life (LCF) region. The fatigue ratio and biofunctionality of these new alloys are much higher than those of the existing biometallic materials. In general, a crack initiates from the surface in the LCF region and from subsurface (internal) in the high cycle fatigue life (HCF) region for the TFC alloy, while, in the case of the TFCA alloy, a crack tends to initiate from the subsurface in both LCF and HCF regions. The internal crack initiation sites are found to be the area with low beta phase stability in the LCF region and at the area with high stability of P phase in the HCF region. The relatively low fatigue strength of TFCA alloy is associated with the addition of Al that leads to precipitate et phase in which both crack initiation and facet formation are easier to occur.

DOI： 10.2320/matertrans.46.1570

Language：English   Publishing type：Research paper (scientific journal)  

Tensile tests and static fracture toughness tests were conducted on dental type 4 gold alloys subjected to various heat treatments. The effects of microstructures on tensile characteristics and static fracture toughness are discussed.
The tensile strength of dental type 4 gold alloy increases with the solutionizing temperature. Moreover, the tensile strength of dental type 4 gold alloy increases with aging time at a solutionizing temperature of 1023 K. On the other hand, dental type 4 gold alloy exhibits reduced elongation with an increase in the solutionizing temperature. Static fracture toughness of dental type 4 gold alloy increases with an increase in the solutionizing temperature.
Static fracture toughness of dental type 4 gold alloy aged for 0.3 ks is the highest, and is the lowest when it is aged for 1.8 ks, with the solutionizing temperature at 1023 K.

DOI： 10.2320/matertrans.46.1540

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.2355/tetsutohagane1955.91.5_485

Language：English   Publishing type：Research paper (scientific journal)  

The mechanical properties of Ti-4.5Al-3V-2Mo-2Fe, a relatively low cost titanium alloy originally designed for structural applications (especially for aerospace applications), were investigated. The alloy was subjected to heat treatments with various solution treatment temperatures (annealing temperature) and cooling rates. The mechanical properties of the heat-treated alloys were then used in order to judge the prospects of practical usage of the alloy for healthcare equipment such as wheelchairs.
The mechanical properties of Ti-4.5Al-3V-2W-Ne are highly affected by either solution treatment or cooling rate, and they change as a result of the change in the microstructure. The alloy single annealed at temperature in the alpha + beta field has very high fatigue ratio (0.80 - 0.85) and high specific strength (210-260 MPa/g cm(-3)) with a modest fracture toughness (J(IC)=25-35 kN/m). This balance of fatigue ratio and specific strength is better than that of the existing wheelchair materials.
Thus, from the point of view of mechanical properties, Ti-4.5Al-3V-2W-2Fe has high potential to be used for healthcare applications. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msec.2004.12.012

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Mechanical properties and microstructures of low cost β titanium alloys for healthcare applications
Titanium alloys are the best choice of metallic materials for biomedical and healthcare applications due to the combination of their excellent mechanical properties and biocompatibility. However, the usage of titanium alloys is limited due to its high cost. In order to reduce their cost, two new titanium alloys, Ti-4.3Fe-7.1Cr (TFC alloy) and Ti-4.3Fc-7.1Cr-3.0Al (TFCA alloy), for healthcare goods such as wheelchairs have been recently developed using low cost ferro-chrom elements. The microstructure and mechanical properties of both alloys subjected to solution treatment in the beta field or thermomechanical treatment were investigated, and then evaluated for their potential to be used as wheelchair materials.
The specific strength and fatigue ratio of TFC and TFCA alloys are much greater than those of the existing wheelchair materials. Unrecrystallized grains obtained in the alloys at low solution treatment temperature can be eliminated by increasing solution treatment temperature or by conducting thermomechanical treatment. The latter method is recommended because it also gives a better strength and ductility balance as a result, mainly, of grain refinement. However, TFCA alloy seems to have more potential to be used as wheelchair materials compared to TFC alloy because of its better workability and post thermomechanical treatment ductility. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msec.2004.12.015

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Beta stabilized new alloys such as Ti-29Nb-13Zr-2Cr, Ti-29Nb-15Zr-1.5Fe, Ti-29Nb-10Zr-0.5Si, Ti-29Nb-10Zr-0.5Cr-0.5Fe and Ti-29Nb-18Zr-2Cr-0.5Si have been developed for dental applications. These alloys were designed based on master alloy Ti-29Nb-13Ta-4.6Zr (TNTZ) for biomedical applications. In this research, high melting temperature element Ta was replaced with beta stabilizing elements such as Cr, Fe and Si to lower the melting temperature of the alloy.
Their melting points, mechanical properties, surface reaction layers and cyto-toxicity were investigated in this study.
Melting points of designed alloys fall by about 50 K to 370 K as compared with that of TNTZ, and Ti-29Nb-13Zr-2Cr has the lowest melting point of around 2050 K. Vickers hardness of the surface of each designed alloy cast into modified magnesia based investment material is in the range of 400 Hv to 500 Hv, which is lower than that of TNTZ (around 560 Hv).
Balances of strength and ductility of cast Ti-29Nb-13Zr-2Cr, Ti-29Nb-15Zr-1.5Fe and Ti-29Nb-10Zr-0.5Cr-0.5Fe are nearly equal to that of cast TNTZ.
Cell viability of each cast designed alloy is excellent. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msec.2005.01.024

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In this study, we investigated the effect of Ta content on the mechanical properties of Ti-30Nb-XTa-5Zr fabricated by a powder metallurgy method, for biomedical applications.
The Ta content ranged from 0&#37; to 20 mass&#37;. The microstructures of Ti-30Nb-XTa-5Zr that contain less than 5 mass&#37; Ta comprise beta phase and an omega phase. The tensile properties of Ti-30Nb-XTa-5Zr change with a change in their deformation mechanisms. The deformation mechanisms of Ti-30Nb-XTa-5Zr, which contains less than 10 mass&#37; Ta, is the stress-induced martensite (SIM) transformation, while that of Ti-30Nb-XTa-5Zr, which contains over 20 mass&#37; Ta, is the slip mechanism. The minimum elastic modulus is obtained in Ti-30Nb-10Ta-5Zr, which comprises a single phase. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msec.2005.04.003

Language：English   Publishing type：Research paper (scientific journal)  

Ti-Nb-Ta-Zr system alloys are receiving more attention for biomedical material component applications. However, the deformation behavior of the Ti-Nb-Ta-Zr system has not been evaluated to date. Therefore, the deformation behavior of Ti-Nb-Ta-Zr alloys with different Nb contents was investigated in this study.
The behaviors of loading-unloading stress-strain curves of Ti-20Nb-10Ta-5Zr and Ti-25Nb-10Ta-5Zr air-cooled after final heating of the manufacturing process are similar to that obtained in metastable beta type titanium alloys that have the shape memory effect. Therefore, the shape memory effect was expected in Ti-20Nb-10Ta-5Zr and Ti-25Nb-10Ta-5Zr alloys. The elastic deformation of Ti-30Nb-10Ta-5Zr disobeyed Hooke's law. However, stress or strain-induced martensite (SIM) is not observed on the loading-unloading stress-strain curve. The deformation mechanism of Ti-25Nb-10Ta-5Zr changes with varying its microstructure. In Ti-25Nb-10Ta-5Zr air-cooled after final heating, the microstructure consisted of an omega phase in a beta phase. The stress for inducing martensite in a phase, am, was nearly equal to the yielding stress, sigma(y). Therefore, stress-induced martensitic transformation and movement of dislocations occurred together. In Ti-25Nb-10Ta-5Zr water-quenched after final heating of the manufacturing process, the microstructure consisted of a single phase, where am is lower than ay, Therefore, stress-induced martensitic transformation occurred before yielding. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msec.2004.12.014

Language：English   Publishing type：Research paper (scientific journal)  

Tensile and plain fatigue properties of P type titanium alloy, Ti-29Nb-13Ta-4.6Zr, which underwent various thermo-mechanical treatments, were investigated in order to judge its potential for biomedical applications.
Microstructures of Ti-29Nb-13Ta-4.6Zr (TNTZ) aged directly at 723 K for 259.2 ks after cold rolling and TNTZ aged at 723 K for 259.2 ks after solution treatment are composed of precipitated alpha phase in beta phase. While, microstructures of TNTZ aged directly at 598 K and 673 K for 259.2 ks after cold rolling and aged at 598 K and 673 K for 259.2 ks after solution treatment are composed of precipitated omega phase, and precipitated alpha and omega phases in beta phase, respectively. Tensile strength of aged TNTZ after solution treatment and aged TNTZ after cold rolling decreases with increasing aging temperature although the elongation shows the reverse trend. TNTZ composed of omega phase or omega and alpha phases in beta phase shows the tensile strength of around 1000 MPa or more. Young's moduli of aged TNTZ after solution treatment and aged TNTZ after cold rolling decrease with increasing aging temperature. TNTZ conducted with solution treatment has the lowest Young's modulus of around 60 GPa. Fatigue strengths of aged TNTZ after solution treatment and aged TNTZ after cold rolling increase with increasing aging temperature. In particular, TNTZ aged directly at 723 K after cold rolling shows the greatest fatigue strength in both low cycle fatigue life and high cycle fatigue life regions, and the fatigue limit, which is around 770 MPa, is nearly equal to that of hot-rolled Ti-6Al-4V ELI conducted with aging, which is one of representative alpha + beta type titanium alloys for biomedical applications. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msec.2004.12.007

Language：English   Publishing type：Research paper (scientific journal)  

Corrosion resistance, wear resistance and biocompatibility of the studied Ti-Ta alloys with Ta contents of 10, 30 and 70 mass&#37; together with the currently used metallic biomaterials pure titanium (Ti) and Ti-6Al-4V extra low interstitial (ELI) alloy were investigated for biomedical applications. Corrosion resistance was measured by an anodic polarization test using an automatic potentiostat in 5&#37; HCl solution at 310 K. Wear resistance was evaluated using a pin-on-disk type friction wear test system with a load of 4.9 N at 310 K in a simulated body fluid (Ringer's solution), and biocompatibility was judged by evaluating the cyto-toxicity through MTT assay. The passive behaviors are observed for all the studied Ti-Ta alloys, and the TiO2 passive films strengthened by the more stable Ta2O5 passive films result in improved corrosion resistance of the studied Ti-Ta alloys with increasing Ta content. All the studied Ti-Ta alloys are non-cytotoxic like pure Ti. The crystal structure shows little influence on the corrosion resistance and cyto-toxicity of the studied Ti-Ta alloys. The experimental results conform the expected excellent corrosion resistance and biocompatibility of the studied Ti-Ta alloys, which are better than or similar to those of pure Ti or Ti-6Al-4V ELI alloy used as standard biomaterials, suggesting their promising potential for biomedical applications. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2005.03.032

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

The authors have realized that solution treatment may be possible at a higher temperature than that by the conventional atmosphere furnace if a fluidized bed furnace is utilized. In this study, solution treatment temperatures close to binary or ternary eutectic temperatures were used for a JIS AC4CH cast aluminum alloy. Mechanical properties were tested with internal microstructures such as micro-pores and intermetallic compound particles then being correlated using high resolution computed tomography. It is clarified that the solution treatment at the ternary eutectic temperature brings the improvement of strength by about 15.7% for a relatively short solution treatment time (typically about 1/10 of the conventional condition by an atmosphere furnace). On the other hand, the solution treatment at the binary eutectic temperature causes significant degradation by coalescence of micro-pores forming crack-like pores. These behaviors can be assessed by visualizing internal microstructures using the high resolution CT. Overall, the combination of the superior heating furnace with the state-of-the-art temperature control and sophisticated visualization technique may enable the improvement of mechanical properties in aluminum cast alloys.

DOI： 10.2464/jilm.55.159

Language：English   Publishing type：Research paper (scientific journal)  

It is known that fracture toughness value of steels is affected by test temperature, specimen thickness and loading rate. In this research, it is attempted to investigate it by changing temperature and loading rate with the rate parameter then being applied. The fracture toughness value is also obtained by round bar specimen with a circular notch. This result has been compared with the results by the CT specimens, and the validity of the fracture toughness value that has been obtained from round bar specimen with a circular notch is examined. The sample material used is HT780 steel. The CT specimens were IT, 2T and 4T-CT defined in ASTM E399, test temperature is varied from 77K to room temperature. The loading rate is also varied for the 1T-CT and the round bar specimen with a circular notch from static to 1 m/s. The fracture toughness value decreases as the test temperature decreases. It decreases with loading rate and specimen thickness. The fracture toughness test result is arranged using the stress intensity factor rate to obtain the rate parameter. Moreover, the fracture toughness value which has been obtained from the round bar specimen with a circular notch is lower than those by 1T-CT specimen, closer to 2T-CT specimen. The test temperature and the loading rate dependency of the fracture toughness value can be arranged by the rate parameter that is the function of temperature and stress intensity factor rate. Availability of the round bar specimen with a circular notch test specimen is discussed to obtain valid fracture toughness values.

DOI： 10.2355/tetsutohagane1955.91.4_415

Language：English   Publishing type：Research paper (scientific journal)